crash on config change after 20.1.2 upgrade

[ctr]

After upgrading to 20.1.2 I have a crash when I save the config (so far only tried in the wireguard section) which results in a reboot, corrupted filesystem and either empty or garbage /conf/config.xml

So far I could only recover by booting into single user mode, running fsck, restoring from and older config and booting again.
Initially I suspected the new kernel, but this is not the case (I just happened to boot off a config.xml which wasn't broken when I tried kernel.old). So my prime candidates would be web-ui writing the config (it immediately kernel panics when I "save") or something in the backend reading it again/processing config templates...