Comment 11 for bug 1946656

I got a bit more insight, subiquity calls `systemctl stop snapd.service`. For some reason the snapd socket is still in use and whatever connection is there, does not become idle, so graceful shutdown eventually fails to close the http server. Eventually snapd is killed by systemd, since it was in a deactivating state and the snapd.service unit state is 'failed'. At this point snap-failure kicks in, stops the snapd.socket unit, and tries to fix things, but since there was no previous revision of the snapd snap or core, it blindly tries to execute /snap/core/current/usr/lib/snapd/snapd. However, the image only has core20 and snapd snaps, there is no 'core'. Thus snap-failure fails, and snapd remain inaccessible.

Open questions is what keeps accessing the snapd socket, so that graceful shutdown fails.