[Matter/Thread] "Failed to process UDP: Security" error when adding Ikea Kajplats bulb with Matter

Configuration Matter/Thread
1

Hello everyone,

I’m unable to add an Ikea Kajplats E14 bulb (Matter/Thread) to my Home Assistant setup.

When connecting through the smartphone, through the matter integration in HA (add a device…), it seems to pass a few steps (I’ve seen something like “creating matter credentials”), but then gets stuck on the step “Verification of connectivity with thread home-assistant”. At this point, the otbr logs show a device trying to connect, but with the following error :

Failed to process UDP: Security

My configuration:

  • Home Assistant: 2026.1.3 (docker installation), OTBR in docker as well
  • Thread Border Router: SMLight SLZB-MR1U (EFR32MG21) connected via USB
  • Thread Network: Active and working with other Apple HomeKit devices (NanoLeaf bulbs)
  • Device: Brand new Ikea Kajplats E14 bulb (never paired before)
  • Integration: Matter (official HA integration)
  • Thread network is used for iOS/Android credentials

What I’ve already tried:

  1. Pairing via smartphone
  2. Verified only 1 border router in HA (and none other connected at home).
  3. Restarted OTBR service
  4. Pairing within 50cm of the border router
  5. Factory reset of the bulb
  6. Thread network is confirmed working (as I have NanoLeaf bulbs working perfectly, but they’re connected through HomeKit and not Matter)

After some digging, I found that people were connecting those bulbs easily through matter so I’m quite suprised, and I didn’t find any suitable solution for this “Failed to process UDP: Security” error.

Any idea what I should look at ?

Thanks in advance !

2

enable ipv6 in homeassistant ?

3

I already have a Thread network active and working (as I’m already using thread bulbs from Nanoleaf), so IPv6 is most likely already enabled.

A little more details on the logs :

OTBR logs while the Bulb tries to connect to the network :

00:05:38.234 [I] MeshForwarder-: Received IPv6 UDP msg, len:90, chksum:c5e1, ecn:no, from:0ee6100c6377cb19, sec:no, prio:net, rss:-62.0, radio:15.4
00:05:38.234 [I] MeshForwarder-: src:[fe80:0:0:0:::***:cb19]:19788
00:05:38.234 [I] MeshForwarder-: dst:[ff02:0:0:0:0:0:0:1]:19788
00:05:38.234 [W] Mle-----------: Failed to process UDP: Security

Matter logs don’t show anything during connection, but I do have some errors before initialization of the server :

2026-02-01 02:02:05.730 (Dummy-2) CHIP_ERROR [chip.native.DIS] Failed to advertise records: src/lib/dnssd/minimal_mdns/Server.cpp:344: CHIP Error 0x00000046: No endpoint was available to send the message

2026-02-01 02:02:05.733 (Dummy-2) CHIP_ERROR [chip.native.DL] Long dispatch time: 250 ms, for event type 2

2026-02-01 02:02:05.761 (MainThread) INFO [matter_server.server.vendor_info] Loading vendor info from storage.

2026-02-01 02:02:05.779 (MainThread) INFO [matter_server.server.vendor_info] Loaded 390 vendors from storage.

2026-02-01 02:02:05.780 (MainThread) INFO [matter_server.server.vendor_info] Fetching the latest vendor info from DCL.

2026-02-01 02:02:05.997 (MainThread) INFO [matter_server.server.vendor_info] Fetched 389 vendors from DCL.

2026-02-01 02:02:05.997 (MainThread) INFO [matter_server.server.vendor_info] Saving vendor info to storage.

2026-02-01 02:02:06.010 (MainThread) INFO [matter_server.server.device_controller] Loaded 0 nodes from stored configuration

2026-02-01 02:02:06.065 (MainThread) INFO [matter_server.server.server] Matter Server successfully initialized.

4

before diving deep into the logs, can you see other tbr in thread settings page ? can you share a screenshot of detected tbr in those page ?

5

Sure, here is the screenshot of the current OTBR :

image
image2052×1340 168 KB

One more information, which might be relevant, is that I migrated my Thread network a few weeks back from an old generic EFR32MG21 generic usb card to my current SMLight MR1U setup. But I haven’t identified any remain of the old network, and the old stick is not connected anymore so I believe it shouldn’t interfere.