Connect ZBT-2 Matter-over-Thread commissioning fails after device joins Thread — repeated NoAck

[colbyjjackson]

Describe the issue you are experiencing

Title: ZBT-2 Matter-over-Thread commissioning fails after device joins Thread — repeated 802.15.4 NoAck

I am unable to commission an IKEA GRILLPLATS Matter-over-Thread outlet using a Home Assistant Connect ZBT-2 and the OpenThread Border Router app.

Environment

• Home Assistant OS 18.2 (amd64 / qemux86-64)
• HAOS is running as a VM on TrueNAS
• Home Assistant Core 2026.8.2
• Supervisor 2026.07.5
• OpenThread Border Router 3.1.1
• Matter Server 9.2.0
• Home Assistant Connect ZBT-2 passed through directly to the HAOS VM
• Android Home Assistant Companion app used for commissioning
• Device: IKEA GRILLPLATS Matter-over-Thread outlet

Problem

Commissioning proceeds normally through discovery and Thread credential provisioning. The Android commissioning flow then reaches:

"Checking connectivity to Thread network"

After waiting, it fails with:

"Can't reach device"

OTBR itself appears healthy. It successfully attaches to the Thread network and becomes leader/primary backbone router:

Mle-----------: Role detached -> leader
[NOTE]-BBA-----: BackboneAgent: Backbone Router becomes Primary!

During a failed commissioning attempt, the IKEA device appears to successfully join the Thread mesh because OTBR allocates another router ID:

RouterTable---: Allocate router id 51

Approximately 2.5 minutes later, OTBR begins reporting repeated failures communicating with that node over 802.15.4:

MeshForwarder-: Failed to send IPv6 UDP msg ... error:NoAck ... radio:15.4

For example:

00:50:57.263 [N] MeshForwarder-: Failed to send IPv6 UDP msg, len:96, chksum:b4e3, ecn:no, to:8ee2208b877047f5, sec:no, error:NoAck, prio:net, radio:15.4
00:50:57.263 [N] MeshForwarder-: src:[fe80:0:0:0:88c4:49ea:7e96:da97]:19788
00:50:57.263 [N] MeshForwarder-: dst:[fe80:0:0:0:8ce2:208b:8770:47f5]:19788

I observed the same pattern on an earlier attempt:

RouterTable---: Allocate router id 59
MeshForwarder-: Failed to send IPv6 UDP msg ... error:NoAck ... radio:15.4
RouterTable---: Release router id 59

Matter Server does not appear to receive the commissioning transaction. It continues to report zero nodes, with no new Matter node appearing during these attempts.

Troubleshooting performed

• Confirmed HAOS VM has a global IPv6 address, IPv6 gateway, and IPv6 is ready
• Confirmed ha docker info reports enable_ipv6: true
• OTBR consistently becomes Thread leader
• Successfully synced HA Thread credentials to Android
• Factory-reset GRILLPLATS before commissioning attempts
• Tested with the GRILLPLATS and Android tablet approximately 6 feet from the ZBT-2
• Initially tested Thread channel 15
• Changed Thread network to channel 25 and confirmed OTBR itself was actually operating on channel 25
• Cleared/rebuilt the stale HA Thread dataset after the channel change and resynced credentials to Android
• Same commissioning failure on channels 15 and 25
• Restarted HA/OTBR/Matter Server during troubleshooting
• Confirmed TREL was enabled with ot-ctl trel
• Temporarily disabled TREL using ot-ctl trel disable and repeated commissioning without restarting OTBR
• Disabling TREL did not change the behavior

The repeated sequence of:

Allocate router id
-> device remains unreachable during Android's Thread connectivity check
-> repeated radio:15.4 error:NoAck
-> commissioning fails

seems potentially significant.

Is this a known ZBT-2/OTBR issue, or is there another diagnostic I can run to determine why the newly joined Thread node becomes unreachable?

What type of installation are you running?

Home Assistant OS

Which operating system are you running on?

Home Assistant Operating System

Which app are you reporting an issue with?

OpenThread Border Router

What is the version of the app?

3.1.1

Steps to reproduce the issue

1. Configure Home Assistant Connect ZBT-2 as the OpenThread Border Router.
2. Confirm OTBR is running and the Thread network is active.
3. Sync the Home Assistant Thread credentials to an Android device.
4. Factory-reset the IKEA GRILLPLATS Matter-over-Thread outlet.
5. In the Home Assistant Android app, select Add Device → Matter and scan the device's Matter QR code.
6. Commissioning begins and reaches "Checking connectivity to Thread network."
7. After waiting, commissioning fails with "Can't reach device."
8. OTBR logs show the device joining/receiving a router ID, followed by repeated MeshForwarder ... error:NoAck ... radio:15.4 messages.

Reproduces consistently, including with the device approximately 6 feet from the ZBT-2 and on Thread channels 15 and 25.

System Health information

System Information

version	core-2026.8.3
installation_type	Home Assistant OS
dev	false
hassio	true
docker	true
container_arch	amd64
user	root
virtualenv	false
python_version	3.14.6
os_name	Linux
os_version	6.18.39-haos
arch	x86_64
timezone	America/New_York
config_dir	/config

Home Assistant Cloud

logged_in	true
subscription_expiration	December 28, 2026 at 7:00 PM
relayer_connected	true
relayer_region	us-east-1
remote_enabled	true
remote_connected	true
remote_server	us-east-1-19.ui.nabu.casa
alexa_enabled	false
google_enabled	false
cloud_ice_servers_enabled	true
certificate_status	ready
instance_id	da4bca4920ae40919b8f87df4dd99f90
iot_state	connected
iot_tries	0
certificate_expire_date	November 14, 2026 at 10:08 PM
certificate_fingerprint	f4801ca28f90b9765285e42316cf6e02f28ccf0d
certificate_alternative_names	undefined
can_reach_cert_server	ok
can_reach_cloud_auth	ok
can_reach_cloud	ok

Home Assistant Supervisor

host_os	Home Assistant OS 18.2
update_channel	stable
supervisor_version	supervisor-2026.07.5
agent_version	1.10.0
docker_version	29.6.2
disk_total	33.7 GB
disk_used	8.8 GB
nameservers	192.168.1.1, 2600:4040:5416:3f00::1
healthy	true
supported	true
host_connectivity	true
supervisor_connectivity	true
ntp_synchronized	true
virtualization	kvm
board	ova
supervisor_api	ok
version_api	ok
installed_addons	Mosquitto broker (7.1.0), Zigbee2MQTT (2.13.0-1), Z-Wave JS (1.7.1), OpenThread Border Router (3.1.1), Matter Server (9.2.0), Terminal & SSH (10.4.0)

Dashboards

dashboards	4
resources	0
views	0
mode	storage

Network Configuration

adapters	lo (disabled), enp0s3 (enabled, default, auto), docker0 (disabled), hassio (disabled), vethe013554 (disabled), veth8509371 (disabled), vethbd29f00 (disabled), veth51fa891 (disabled), veth60077e1 (disabled), veth3908378 (disabled), vethe780392 (disabled), vethcb693f8 (disabled), veth0d771e6 (disabled), veth9c88b40 (disabled), wpan0 (disabled)
ipv4_addresses	lo (127.0.0.1/8), enp0s3 (192.168.1.174/24), docker0 (172.30.232.1/23), hassio (172.30.32.1/23), vethe013554 (), veth8509371 (), vethbd29f00 (), veth51fa891 (), veth60077e1 (), veth3908378 (), vethe780392 (), vethcb693f8 (), veth0d771e6 (), veth9c88b40 (), wpan0 ()
ipv6_addresses	lo (::1/128), enp0s3 (2600:4040:5416:3f00:15c9:64b9:98da:2893/64, fe80::93f0:3a91:8eaa:fed3/64), docker0 (fd4d:1580:d6e7::1/64, fe80::ec67:21ff:fe14:a2e6/64), hassio (fd0c:ac1e:2100::1/48, fe80::3cf1:9fff:feed:8fdf/64), vethe013554 (fe80::6cd9:b8ff:fe63:9086/64), veth8509371 (fe80::b0f6:29ff:fec9:5d83/64), vethbd29f00 (fe80::54dd:53ff:fee1:a4b6/64), veth51fa891 (fe80::c87b:1bff:fe77:10ba/64), veth60077e1 (fe80::802c:28ff:fe32:e04b/64), veth3908378 (fe80::40b3:d4ff:fe6b:4147/64), vethe780392 (fe80::48ca:e2ff:fe10:c29/64), vethcb693f8 (fe80::a8c5:bfff:fee6:3012/64), veth0d771e6 (fe80::dc36:e0ff:fe67:1424/64), veth9c88b40 (fe80::80f5:48ff:fe09:48a4/64), wpan0 (fd02:33a9:d0eb:ac66:0:ff:fe00:fc11/64, fd0a:1a71:3d07:1:3d98:81ec:9e96:a692/64, fd02:33a9:d0eb:ac66:0:ff:fe00:fc38/64, fd02:33a9:d0eb:ac66:0:ff:fe00:fc10/64, fd02:33a9:d0eb:ac66:0:ff:fe00:fc00/64, fd02:33a9:d0eb:ac66:0:ff:fe00:5000/64, fd02:33a9:d0eb:ac66:8333:603e:fa4e:c565/64, fe80::88c4:49ea:7e96:da97/64)
announce_addresses	192.168.1.174, 2600:4040:5416:3f00:15c9:64b9:98da:2893, fe80::93f0:3a91:8eaa:fed3

Recorder

oldest_recorder_run	August 1, 2026 at 12:38 PM
current_recorder_run	August 22, 2026 at 9:43 AM
estimated_db_size	12.99 MiB
database_engine	sqlite
database_version	3.53.2

Anything in the Supervisor logs that might be useful for us?

2026-08-16 12:07:49.899 WARNING (MainThread) [homeassistant.components.otbr.config_flow] Failed to communicate with OTBR@http://core-openthread-border-router:8081: Cannot connect to host core-openthread-border-router:8081 ssl:default [Timeout while contacting DNS servers]
2026-08-16 12:12:09.795 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Input source "TV" for entity: media_player.tx_rz50 is not in the list. Check integration options
2026-08-16 12:12:09.832 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Listening mode "DOLBY SURROUND THX CINEMA ··· PLII/PLIIx THX CINEMA" for entity: media_player.tx_rz50 is not in the list. Check integration options
2026-08-16 12:12:10.074 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Input source "MAIN SOURCE" for entity: media_player.tx_rz50_zone_2 is not in the list. Check integration options
2026-08-16 12:12:10.197 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Input source "MAIN SOURCE" for entity: media_player.tx_rz50_zone_3 is not in the list. Check integration options
2026-08-16 12:12:13.959 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Input source "TV" for entity: media_player.tx_rz50 is not in the list. Check integration options
2026-08-16 12:12:13.999 WARNING (MainThread) [homeassistant.components.onkyo.media_player] Listening mode "DOLBY SURROUND THX CINEMA ··· PLII/PLIIx THX CINEMA" for entity: media_player.tx_rz50 is not in the list. Check integration options

Anything in the app logs that might be useful for us?

[08:04:11] INFO: Starting otbr-agent...
[NOTE]-AGENT---: Running 0.3.0-ec16e396
[NOTE]-AGENT---: Thread version: 1.4.0
[NOTE]-AGENT---: Thread interface: wpan0
[NOTE]-AGENT---: Radio URL: spinel+hdlc+uart:///dev/serial/by-id/usb-Nabu_Casa_ZBT-2_E072A1D8B134-if00?uart-baudrate=460800&uart-flow-control
[NOTE]-AGENT---: Radio URL: trel://enp0s3
[NOTE]-ILS-----: Infra link selected: enp0s3

00:00:08.276 [N] Mle-----------: RLOC16 5000 -> fffe
00:00:08.986 [N] Mle-----------: Attach attempt 1, AnyPartition reattaching with Active Dataset
00:00:15.537 [N] Mle-----------: Attach attempt 1, AnyPartition reattaching with Pending Dataset
00:00:22.040 [N] RouterTable---: Allocate router id 20
00:00:22.040 [N] Mle-----------: RLOC16 fffe -> 5000
00:00:22.042 [N] Mle-----------: Role detached -> leader
00:00:22.043 [N] Mle-----------: Partition ID 0x746b4fd
[NOTE]-BBA-----: BackboneAgent: Backbone Router becomes Primary!

00:48:15.413 [N] RouterTable---: Allocate router id 51

00:50:57.263 [N] MeshForwarder-: Failed to send IPv6 UDP msg, len:96, chksum:b4e3, ecn:no, to:8ee2208b877047f5, sec:no, error:NoAck, prio:net, radio:15.4
00:50:57.263 [N] MeshForwarder-:     src:[fe80:0:0:0:88c4:49ea:7e96:da97]:19788
00:50:57.263 [N] MeshForwarder-:     dst:[fe80:0:0:0:8ce2:208b:8770:47f5]:19788

00:50:58.326 [N] MeshForwarder-: Failed to send IPv6 UDP msg, len:96, chksum:f4bb, ecn:no, to:8ee2208b877047f5, sec:no, error:NoAck, prio:net, radio:15.4
00:50:58.326 [N] MeshForwarder-:     src:[fe80:0:0:0:88c4:49ea:7e96:da97]:19788
00:50:58.326 [N] MeshForwarder-:     dst:[fe80:0:0:0:8ce2:208b:8770:47f5]:19788

00:50:58.895 [N] MeshForwarder-: Failed to send IPv6 UDP msg, len:96, chksum:f961, ecn:no, to:8ee2208b877047f5, sec:no, error:NoAck, prio:net, radio:15.4
00:50:58.895 [N] MeshForwarder-:     src:[fe80:0:0:0:88c4:49ea:7e96:da97]:19788
00:50:58.895 [N] MeshForwarder-:     dst:[fe80:0:0:0:8ce2:208b:8770:47f5]:19788

Additional information

No response