Matter / Thread Issues: Cannot remove old Google Nest Preferred Network

[tender frost]

Update: I don't know why or how, but I tried adding a matter device a day later and it appears to have added successfully. The only event between the two that I can think of was a router & switch reboot. For reference this is how my thread network ended up looking

[tender frost]

Update again: Initially I was able to connect a few devices, now some hours later we're back to the initial behavior