The Short Answer: Slow Is Not the Same as Broken

Home Assistant Matter Server 9 can remain on “Starting” while it performs a real one-time migration. The safe response is to read the Matter Server log before restarting anything. If the log is moving through storage migration, loading nodes, and device interviews, leave it alone. An interview is the controller rereading each device's features and current information. There is no official fixed timeout, so a stopwatch cannot tell you whether the job is stuck.

If the same startup sequence begins again and again, first update the Matter Server app to the newest stable 9.0.x release offered by Home Assistant, turn off the app's Watchdog for this migration, and give it one uninterrupted attempt. Watchdog is the Supervisor switch that restarts an unhealthy app. That is useful normally, but the original health check could restart a valid long migration before it finished. As of July 10, 2026, the stable changelog lists 9.0.4.

The Matter Server is the separate local controller behind Home Assistant's Matter integration. A slow migration does not mean every plug, bulb, lock, or sensor needs a new identity. Do not factory-reset devices, delete the integration, or uninstall the app as an early fix.

House-safety boundary: before maintenance, make sure exterior locks, garage doors, alarms, leak shutoffs, heating or cooling, and critical lights have a tested manual fallback. Avoid changing the smart-home controller while nobody can reach the home.

Why So Many People Saw “Starting” or “Matter Offline”

Home Assistant released Matter Server app 9.0 on June 23, 2026. It replaced the older Python-and-C++ controller with a matter.js-based server, migrated existing controller data automatically, and moved Home Assistant to Matter 1.5.1. The new design promises faster later starts, faster reconnection, better over-the-air updates, and a new Thread and Wi-Fi network view.

The quick follow-up patches show why the exact version matters: 9.0.1 fixed the default-port health check, 9.0.2 allowed more time for health checks, and 9.0.4 bundled further issue fixes plus substantial RAM and CPU optimization. Use a newer stable version if Home Assistant offers one after this article's July 10 publication date.

The first start is intentionally different. It converts the old storage, loads the existing Matter devices, and performs a full interview. The official migration FAQ also says the new server uses roughly twice the RAM of the old one and somewhat more CPU. Early 9.0.0 health checks, long migrations, and resource pressure produced several symptoms that looked identical from the dashboard.

The demand was immediate. An r/homeassistant release thread received dozens of votes and reports of 20-to-45-minute waits, restart loops, and Matter showing offline. A Home Assistant Community question asked where the Watchdog setting even lived. GitHub issue 4661 captured a 9.0.0 crash loop. Those reports establish the homeowner problem; the fix order below comes from the official changelog, migration FAQ, and current Home Assistant docs.

Three network terms in plain English: mDNS is the local announcement service devices use to tell Home Assistant where they are. IPv6 is the local addressing Matter uses inside the house. A Thread border router is the powered device that connects the low-power Thread network to the regular home network.

If You Have Not Upgraded Yet

  1. Update Home Assistant itself first. Home Assistant's Matter docs tell users to run the latest Home Assistant version before adding or maintaining Matter.
  2. Create a manual backup. Go to Settings > System > Backups, choose Backup now, and include the Matter Server app and configuration. Download a copy to another computer or backup location and keep the emergency kit needed to restore encrypted backups.
  3. Record the versions. Note Home Assistant Core, OS, Supervisor, Matter Server, and OpenThread Border Router versions. If recovery is needed, this saves guesswork.
  4. Check resource headroom. A host already short on memory has less room for the one-time conversion and full device interview. There is no official universal RAM minimum for every home, so look for actual pressure instead of guessing from device count.
  5. Turn Beta off. The old beta flag can remain enabled after the change to 9.0. Stable 9.0.4 is the normal recovery path; a newer upstream beta is not automatically safer.
  6. Temporarily disable Watchdog. Open Settings > Apps > Matter Server and switch off Watchdog for the initial 8.x-to-9.x migration.
  7. Install the current stable update and open the log. Let the first start finish without repeated restarts. Re-enable Watchdog only after the controller has started reliably.

If Matter Server Is Already Stuck on Starting

  1. Protect what remains. First verify and download the pre-update backup. If no pre-update backup exists, make a current backup before more experiments; it will not undo the failed upgrade, but it preserves the remaining controller state and evidence. Save the Matter Server and Supervisor logs. If the integration still opens, use Settings > Devices & services > Matter and download diagnostics from its menu.
  2. Check the app version and channel. If it is 9.0.0 through 9.0.3, install stable 9.0.4 or any newer stable release Home Assistant now offers. Turn Beta off unless a maintainer has explicitly asked you to test it.
  3. Disable Watchdog for the migration attempt. This prevents an early health check from repeatedly killing a valid conversion. It does not cure low memory or a software crash.
  4. Start the app once and watch the log. Changing migration messages, new node numbers, or continuing device interviews are progress. Leave them alone. The same opening lines repeating from the top indicate a restart loop.
  5. Wait for the controller to start and the interview to finish. The app may become available before every sleepy Thread sensor has checked in. Do not declare failure because one battery device is late.
  6. Re-enable Watchdog after a stable start. Then make a new post-migration backup so the recovered state is protected.
What you see What it usually means Best next step
Starting, with new log lines appearing The one-time storage migration or full device interview may still be working. Wait. Judge by log progress, not a fixed number of minutes.
Starting, with the same startup repeated Watchdog, a health check, a crash, or memory pressure may be restarting the app. Use current stable 9.0.x, turn Beta off, disable Watchdog only for migration, and inspect the final lines before each restart.
App says Running; Home Assistant says Matter offline The controller started, but the Home Assistant integration may not have reconnected. Allow interviews to finish. Then try one controlled Home Assistant or Matter app restart and collect diagnostics if the mismatch remains.
One or a few devices remain offline Those devices may not have announced their address through local mDNS yet. Wake or safely power-cycle one affected device. Do not reset it.
All Thread devices offline; Wi-Fi Matter works The Thread border router, Thread network, IPv6, or multicast path is the likely shared fault. Check the Thread page, border-router power, local IPv6, mDNS, and network isolation.
Exit code 137 or heap-out-of-memory errors Possible host memory pressure or a server memory problem, not a pairing problem. Preserve logs, check memory use, reduce nonessential workloads or add headroom, and escalate if growth continues.

How to Read the Log Without Becoming a Developer

You do not need to understand every technical line. Look for the story the log tells.

  • Progress: the log moves from storage migration into loading different Matter device records, called nodes, then device interviews, then a message that the Matter controller started.
  • Restart loop: the banner and earliest startup messages repeat, with the same devices beginning again. Note the final warning or error before each restart.
  • Discovery problem: messages such as Resolving (no address known) suggest the server cannot discover a device's current local address.
  • Network problem: Network is unreachable, repeated failures to make a secure Matter connection, or every device of one network type disappearing points to the local path rather than forty simultaneous accessory failures.
  • Memory problem: Supervisor exit code 137, host memory-pressure messages, or JavaScript heap errors—meaning the server ran out of working memory—deserve a resource investigation. Do not hide them by assigning an arbitrary larger memory limit.

Community migrations have taken roughly ten minutes in one setup and much longer in others. Those examples are useful reassurance, not an official deadline. A changing log is the better signal.

If the Server Runs but Devices Stay Offline

Start with one device, not the whole house. The official migration FAQ says devices left offline after the first start are often not announcing themselves through mDNS, the local discovery service that tells the controller where a device lives. Safely wake a battery device according to its manual, or power-cycle one plug or bulb only if the connected load can be interrupted. Once Server 9 learns an address, it can also retry the last known address later.

Then separate the failure by network type. If Matter-over-Wi-Fi devices work but every Matter-over-Thread device is offline, check the Thread border router—the powered device that connects the low-power Thread mesh to the home network. Also check that Home Assistant's Thread page still shows the intended network and that the border router is reachable. Do not create a second Thread network to solve an outage on the first.

If Wi-Fi and Thread Matter devices are both offline, focus first on the Matter app, integration connection, and local network. Home Assistant's official Matter docs require IPv6 to be enabled on the Home Assistant host and multicast traffic—the local announcements sent to nearby devices—to reach it. This is local IPv6; it does not require an IPv6 internet service. If unsure, the docs recommend setting IPv6 to Automatic under Settings > System > Network. Guest Wi-Fi, client isolation, firewalls, or a VLAN, an advanced separate network segment, can block the local mDNS and IPv6 traffic Matter needs.

What to Do About High RAM or CPU

The first migration and full interview naturally do more work than a normal start. The official FAQ also warns that Server 9 needs roughly twice the memory of the old server and a little more CPU. Version 9.0.4 includes resource optimizations, so stable 9.0.4 is the first ordinary update step.

After migration, look at the pattern. A temporary peak that falls after all devices return is different from memory that grows until the app exits. A July 2026 GitHub report describes exit code 137 on a 4 GB virtual machine, but that single case does not establish a universal 6 GB minimum. Use the host's actual memory pressure, logs, device count, and other running apps as evidence.

If the app keeps being killed, stop the restart experiment, preserve logs, make sure the backup is accessible off the Home Assistant host, and report the exact versions and error. Temporarily stopping nonessential heavy apps or moving Home Assistant to supported hardware with more headroom can help a constrained host. Blindly raising the server's working-memory limit can let one process consume the rest of the machine and is not a safe homeowner fix.

What Not to Do

  • Do not factory-reset devices in bulk. One controller or network fault should not become dozens of new Matter identities and pairing jobs.
  • Do not uninstall and reinstall Matter Server or the Matter integration as a routine fix. That can discard the very controller state the migration is trying to preserve.
  • Do not repeatedly restart an advancing migration. It may force the app to redo work and can create the loop you are diagnosing.
  • Do not leave Watchdog off permanently. Its temporary pause is for the first migration, not a way to hide later crashes.
  • Do not turn on Beta because its version number is newer. Beta is a pre-release test path. Use it only with a verified backup and explicit issue-specific guidance.
  • Do not disable IPv6, block multicast, or create a new Thread network during recovery. Those changes remove communication paths Matter needs.
  • Do not paste destructive storage-deletion commands from a forum into a generic outage. The official FAQ has one directory-deletion procedure for one exact fabric-authority error. That expert exception requires the exact error, a verified backup, and preferably maintainer help.

After the Migration Succeeds

  1. Turn the Matter Server Watchdog back on.
  2. Open Settings > Apps > Matter Server > Open Web UI and confirm the expected nodes appear.
  3. Test at least one Wi-Fi Matter device and one Thread Matter device if the home has both.
  4. Check important automations and manual controls instead of assuming that an available device means every action works.
  5. Review any device that still lacks energy, event, or sensor entities before re-pairing it; record its model, firmware, and diagnostics.
  6. Create and download a new backup labelled as the successful post-migration state.

The Official Support Boundary

This guide applies to the official Matter Server app on Home Assistant OS. Home Assistant's current Matter documentation says that is the only supported Matter app installation. A custom Docker Matter server can work, but its storage paths, networking, health checks, and recovery steps are different and at the user's own risk. Do not apply the app's Watchdog or restore steps to a custom container without its own documentation.

The daily Matter control path remains local: Home Assistant talks to Matter devices inside the house. Server 9 can update certificate and vendor information in the background and some commissioning or firmware jobs can use internet access, but an internet warning alone does not prove that established in-home device control has become cloud-dependent.

Tara's Practical Recommendation

Treat Matter Server 9 as a controlled data migration, not an accessory reset event. Start with a downloadable backup, current stable software, Beta off, enough memory headroom, and Watchdog temporarily disabled. Let the log prove whether work is progressing. After the controller starts, recover one device and one network path at a time.

If stable 9.0.4 or a newer stable release cannot complete with Watchdog off and adequate resources, stop. Preserve logs and diagnostics, use the pre-upgrade backup through Home Assistant's restore flow, or ask for issue-specific maintainer guidance. The official FAQ says there is no simple switch back to the old Python server, which is exactly why the backup comes before experimentation.

FAQ

How long should the first Matter Server 9 start take?

Home Assistant does not publish a fixed timeout. Leave the server alone while the log is advancing through storage migration and device interviews. A repeating startup sequence or an unchanged error is different from slow progress.

Should Watchdog stay disabled after the Matter Server 9 upgrade?

No. Disable the Matter Server app Watchdog only long enough for the first 8.x-to-9.x migration to finish, then turn it back on after a stable start.

Do Matter devices need to be paired again after upgrading to Server 9?

Normally no. Server 9 is designed to migrate the existing controller data automatically. Do not factory-reset or remove devices just because the first start is slow or they briefly appear offline.

What if Matter Server is running but devices remain offline?

Safely wake or power-cycle one affected device so it announces itself again, then check local mDNS discovery, IPv6, and the Thread border router if Thread devices are affected. Do not reset the device.

Can you switch Matter Server 9 back to the old Python server?

There is no normal supported toggle back to the old server. Keep a verified pre-upgrade backup and use Home Assistant's restore flow or maintainer guidance if the current stable release cannot complete the migration.