ZBT-2 - Not able to add new devices

Configuration Matter/Thread
1

I’m having issues with Matter over Thread in my Home Assistant setup. I’ve been trying for weeks now reading on forums and debugging my setup. But nothing works…

I started with a Sonoff ZBDongle-E (the right version for Thread) but could not get it to add new devices. Figured I got the wrong version after a lot of discussion with Chat GPT. So I gave up and ordered the ZBT-2 thinking that there was no chance it would not work.

To start with I had issues installing the Thread firmware through the companion app. Solved that and all add-ons and integrations installed fine. Everything looks fine but I have some troubles to sync credentials. I start in settings for the companion app > Troubleshooting > Thread and sync credentials. Then I go to Integrations > Thread and send credentials to Home Assistant and then to my phone (IOS). Sometimes it works, but most of the time I get “Thread network credentials does not match with any of the active thread networks around”.

When the credential sync works, I can start the process to add a new device through the matter integration. Sometimes it says connecting and then configuring but then it says that the device cannot be added. Most of the time it stays on connecting. I’ve only tried with IKEA myggbett since that’s the only Matter over Thread device i got so far.

I have tried to remove everything and then add again, manually reinstalling firmware, tried different USB outlets, countless different settings. I have read ALL issues posted online. What am I doing wrong?

My setup: HAOS 2026.2.2 on a TrueNAS server. iPhone running IOS 26.2.1

I get some concerning logs in OTBR:
00:00:37.426 [W] DuaManager----: Failed to perform next registration: NotFound

00:01:03.853 [N] MeshForwarder-: Failed to send IPv6 UDP msg, len:178, chksum:fcf6, ecn:no, to:9eb255ccb9e53801, sec:yes, error:NoAck, prio:net, radio:all
…
00:01:08.204 [W] P-RadioSpinel-: Error processing result: NoAddress

00:01:08.204 [W] P-RadioSpinel-: Error waiting response: NoAddress

2

Solved it finally!

The root cause of the problem was that the host (TrueNAS Scale) did not pass through IPv6-traffic/messages correctly from the VM (HAOS) to the rest of the network. Though my understanding of IPv6 is limited.

I figured this out, with help from ChatGPT, when I could only see the service _meshcop._udp. sporadically on my iPhone. The solution was to add a dedicated NIC and pass it through to Home Assistant OS (not NIC passthrough, PCI passthrough). Previously the host and VM shared one network interface.

Then i had to reset the border router in the Thread integration to get a new network name and PAN-ID to get it to work.

I hope this can be of help to others experiencing similar issues.