I was able to reproduce what might be the same issue using a near default version of the template app in nrf connect. See the discussion here: XIAO nrf54l15 Matter App Recipe. (Didn’t publish that info here since it seemed like a nice recipe, and I didn’t want it to get lost in this discussion.)
I have a raytac board arriving today. I’m going to see if I can reproduce it there. After that I might put on my big boy boots and dive in with the debugger again.