Extremely unstable device commissioning with basic_thread_border_router example

[schildbach]

I'm running the basic_thread_border_router example on an "ESP Thread Border Router/Zigbee Gateway V1.2" dev board. Except for hardcoding my Wifi credentials, enabling OPENTHREAD_BR_AUTO_START and setting my TLV via console, I'm using the default configuration. I currently have 10 devices commissioned (took many attempts!) and once commissioned they work reasonably well.

However,
when I try to commission new Thread devices via Home-Assistant 2026.6 / matterjs-server 0.8.0 / ESPHome 2026.5, only one out of twenty commissioning attempts succeed. The BLE phase is always successful, but then Thread IPv6 communication seems to drop packets on a larger scale. I see this in the console:

W(142605) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(143355) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(144115) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(145365) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(146625) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(147875) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(149405) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(150165) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(151425) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(153525) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(154275) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(155545) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(158155) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(158915) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(160175) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(163765) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(164525) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(165785) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(171395) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(172145) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(173405) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(183015) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(183765) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(202665) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(203425) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(204685) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
I(219915) OPENTHREAD:[N] MeshForwarder-: Failed to send IPv6 UDP msg, len:425, chksum:8119, ecn:no, to:0x4805, sec:yes, error:NoAck, prio:normal
I(219915) OPENTHREAD:[N] MeshForwarder-:     src:[2a02:3100:28a6:7a00:2a0c:50ff:fe6d:3fe4]:60655
I(219915) OPENTHREAD:[N] MeshForwarder-:     dst:[fd61:c658:cd0b:1:a9ff:a50b:660f:36a9]:5540
W(238385) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(239145) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(240405) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
I(250455) OPENTHREAD:[N] MeshForwarder-: Failed to send IPv6 UDP msg, len:425, chksum:8119, ecn:no, to:0x4805, sec:yes, error:NoAck, prio:normal
I(250455) OPENTHREAD:[N] MeshForwarder-:     src:[2a02:3100:28a6:7a00:2a0c:50ff:fe6d:3fe4]:60655
I(250455) OPENTHREAD:[N] MeshForwarder-:     dst:[fd61:c658:cd0b:1:a9ff:a50b:660f:36a9]:5540
W(306245) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(306995) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(308255) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(438355) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(439105) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs
W(440365) OPENTHREAD:[W] Mle-----------: Failed to process Parent Request: NoBufs

After some research, I tried a few configuration changes on the esp32s3:

CONFIG_SPIRAM=y
CONFIG_SPIRAM_TRY_ALLOCATE_WIFI_LWIP=y

OPENTHREAD_CONFIG_NUM_MESSAGE_BUFFERS=256

Those did not help. I tried a few other changes on the RCP (esp32h2):

OPENTHREAD_SPINEL_RX_FRAME_BUFFER_SIZE=2048
OPENTHREAD_UART_BUFFER_SIZE=4096

Those made the RCP unstable (frequent crashes), so I reverted them quickly.

Can someone suggest specific configuration changes that will help? Will there be a new version in this repo? I see the last version is from December 2025, and there were only cosmetic changes since then.