I run a pure IKEA Matter-over-Thread setup in Home Assistant. No Zigbee, no other Matter vendors, no bridges — every single node in the network is IKEA of Sweden, all on current firmware.

Router nodes (mains powered) — 19

• 14x GRILLPLATS plug
• 2x KAJPLATS E27 WS globe 1521lm
• 2x KAJPLATS GU10 CWS 470lm
• 1x KAJPLATS E14 WS B38 CL 470lm

Sleepy end devices (battery) — 20

• 8x TIMMERFLOTTE temperature/humidity sensor
• 5x MYGGBETT door/window sensor
• 3x KLIPPBOK water leak sensor
• 2x MYGGSPRAY motion sensor
• 2x BILRESA dual button

The problem

Every day, 1-3 random devices go unavailable in Home Assistant. Some come back on their own after roughly 10 minutes. Others never come back until I power cycle them or re-pair.

There is no pattern I can find. It's not the same devices, not the same room, not the same product type, not the same time of day. Mains-powered routers drop just as often as battery end devices.

What I've already ruled out

Border router. I've tried an SLZB-06, an SLZB-06M and an SLZB-06MU, both with OTBR running on the device and with a remote OTBR. Exactly the same behaviour in every combination, so I don't believe the BR itself is the fault.

Link quality / mesh edges. Nothing is sitting at the edge of the mesh. Every node has at least 3 links to other routers.

Wi-Fi channel overlap. Thread is on channel 20, my APs are on 1, 6 and 11. More importantly, devices drop from every room in the building rather than one specific area, so localised RF interference doesn't fit the symptoms either.

IPv6 / mDNS. The network works fine the rest of the time, so I'm assuming both are basically functional — though I'd happily be told what specifically I should be testing here instead of assuming.

The part that makes the least sense

I run essentially the same setup at a second location: SLZB border router, IKEA-only Matter devices, full UniFi stack. That one has not dropped a single device in over three months. Completely rock solid.

Same vendor, same border router family, same network gear, same Home Assistant. One site is flawless, the other loses devices daily. So whatever this is, it looks site-specific rather than a general "IKEA firmware is bad" problem — I just can't work out which variable is the one that matters.