I don't know what I did, but after rebooting my router I find myself in this strange situation:
The router boots
it brings up wireless networks
My devices connected through wifi or cable get a lease from DHCP
it's impossible to ping the router IP or SSH it or access internet from the LAN
The WAN is up, I can ping it from another network, I can SSH into it. I have an IPv6 tunnel on this router and it works as well and is accessible from the internet.
I have a wireguard interface and I can access the LAN from the internet through wireguard. From there I can even connect to Luci.
Once connected through wireguard I can access everything in the router, use its resources as if I were on my LAN, the internet connection goes through it perfectly fine.
So it's really just the LAN that is inaccessible. Both wifi and cable.
What should I look at in order to diagnose what is wrong?
I have looked at the firewall and network interfaces and see no change from before this situation.
I sometimes have similar symptoms when bridges change composition, and end up with a different MAC-address than before. This causes the ARP-cache on client devices to contain invalid values, that then have to first "age out". This can take 3-10 minutes.
Since your message is older that that, i assume, you have a different problem. Just wanted to throw this datapoint about similar symptoms out there.