Thread panel loses border router after ~3 minutes – OTBR on external device (SLZB-06), network fully functional

[sahomm]

The problem

The Thread panel in HA shows "No border router found" for the preferred network (OpenThread-1199), even though the OpenThread Border Router running on an SMLIGHT SLZB-06Mg26U is fully functional and reachable via REST API and mDNS.

After rebooting the SLZB, the Thread panel correctly shows the border router for approximately 3–4 minutes. After that it disappears and the panel shows "No border router found" permanently – until the next reboot. Thread devices continue to work normally throughout the whole time.

When trying to manually add the OTBR integration (Settings → Integrations → Add → OpenThread Border Router), HA responds with "The Thread Border Router is already configured", which confirms a config entry exists but is apparently not used to keep the Thread panel updated.

The credential transfer to the HA Companion App only works during the short window after reboot while the panel still shows the border router.

I verified extensively that the issue is on the HA side, not the network or the device:

1. OTBR REST API reachable and healthy (tested from Debian host in same VLAN):

curl http://192.168.120.180:8080/node
{"NetworkName":"OpenThread-1199","ExtPanId":"d7fb196509929fa5","ExtAddress":"ced034e7c1f3b32c","RlocAddress":"fdf9:fdce:3930:7cf3:0:ff:fe00:f000","LeaderData":{"PartitionId":913992751,"Weighting":64,"DataVersion":46,"StableDataVersion":118,"LeaderRouterId":48},"State":3,"Rloc16":61440,"NumOfRouter":2}

curl http://192.168.120.180:8080/node/state
"router"

2. mDNS announcement correct and complete (avahi-browse from same VLAN):

= eth0 IPv4 SLZB-06Mg26U   _meshcop._udp   local
   hostname = [SLZB-06Mg26U.local]
   address  = [192.168.120.180]
   port     = [49154]
   txt      = ["dn=DefaultDomain" "tv=1.4.0" "nn=OpenThread-1199" "mn=BorderRouter" "vn=OpenThread" "rv=1" "bb=\240\191" "sq=5" "pt=6zl/" "at=\000\000\000\000\000\000\000\002" "sb=\000\000\009\177" "xa=\206\2084\231\193\243\179," "xp=\215\251\025e\009\146\159\165" "omr=@\253\254\246_f\151\000\001" "id=i\196\231\166]\029\246\170\031n\002W\028\180\134\222"]

The id= TXT field is present. Record is announced on both IPv4 and IPv6.

3. All Thread devices work normally regardless of what the panel displays.

Network config: dedicated IoT VLAN (192.168.120.0/24), HA has dedicated NIC in this VLAN, SLZB connected via Ethernet. IGMP Snooping off, MLD Snooping off, multicast blocker off, client isolation off.

The Thread panel seems to rely exclusively on live mDNS/zeroconf cache to display border routers, independent of the configured OTBR integration. Once the mDNS cache entry expires, the panel loses the border router – even though the REST API is still reachable and the mDNS record is still being announced by the device (confirmed via avahi-browse from an external host at the same time HA shows "no border router

What version of Home Assistant Core has the issue?

2026.6.4

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant OS

Integration causing the issue

Thread / OpenThread Border Router

Link to integration documentation on our website

https://www.home-assistant.io/integrations/thread/

Diagnostics information

404: Not Found

Example YAML snippet

Anything in the logs that might be useful for us?

Additional information

The OTBR is running directly on the SLZB device (Option B – Thread+OTBR running on device, no OTBR add-on installed in HA). SLZB firmware: 20260416 / v3.3.3.dev4.

A second border router (Amazon Echo Studio) is present in the same VLAN on a completely separate Thread network (nn=AMZN-Thread-f72d, different ExtPanId). It is not configured in HA and is unrelated to this issue.

[home-assistant]

Hey there @home-assistant/core, mind taking a look at this issue as it has been labeled with an integration (thread) you are listed as a code owner for? Thanks!

Code owner commands

Code owners of thread can trigger bot actions by commenting:

• @home-assistant close Closes the issue.
• @home-assistant rename Awesome new title Renames the issue.
• @home-assistant reopen Reopen the issue.
• @home-assistant unassign thread Removes the current integration label and assignees on the issue, add the integration domain after the command.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component, problem in config, problem in device, feature-request) to the issue.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component, problem in config, problem in device, feature-request) on the issue.

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@sahomm Thanks for reporting this issue!

Before we dive in, please make sure this isn't a duplicate by searching through existing issues. Also check recently closed issues, as your problem might already be fixed but not yet released.

https://github.com/home-assistant/core/issues?q=%20label%3A%22integration%3A%20thread%22%20
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thread documentation
thread source
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[sahomm]

This appears related to #173300 which was closed. However, in my case OTBR
runs directly on the SLZB-06Mg26U device (not as an HA add-on), and I am
on 2026.6.4 where the issue still persists. The setup difference may be
relevant – the mDNS announcement from the device is confirmed working from
an external host at the same time HA shows "No border router found".

Additional finding: On a fresh HA instance in the same VLAN/subnet,
the SLZB-06Mg26U border router is discovered correctly and remains
visible under "Other networks". The issue only occurs once the network
is set as the preferred network. This suggests the bug is in how HA
handles mDNS refresh specifically for the preferred network, not in
discovery itself.

[mrvanes]

I see exactly the same behaviour on HA 2026.6.4 and can add that I can restore functionality (visible OTBR router in Thread configuration)

1. By restarting the OTBR container
2. By requesting mDNS discovery of the _meshcop._udp type using avahi-browse on a laptop in the same network:

$ avahi-browse -r -t _meshcop._udp
+ wlp64s0 IPv6 Home Assistant OpenThread Border Router b6136c5e45ee5096 _meshcop._udp        local
= wlp64s0 IPv6 Home Assistant OpenThread Border Router b6136c5e45ee5096 _meshcop._udp        local
   hostname = [kronos-otbr.local]
   address = [fe80::f6b5:20ff:fe13:23d7]
   port = [49154]
   txt = ["mn=OpenThread Border Router" "vn=Home Assistant" "omr=@\253]\133\135Q\168\000\001" "dn=DefaultDomain" "bb=\240\191" "sq=S" "at=\000\000\000\000\000\001\000\000" "pt=\026\163/\008" "nn=ha-thread-440c" "xp=\159\153\156E\212\219\211\250" "xa=\182\019l^E\238P\150" "tv=1.4.0" "sb=\000\000\031\177" "rv=1" "id=\188'\168\206\153\215\254\030\169\030Q)\2549U\000"]