So I realized today that Immich is in a reboot loop.
There's no clear error in the log - the last log is always "server is running"; followed by geodata import, followed by immich-server rebooting.
I'm not sure how long this has been going on (I don't check immich daily), It's supposedly running v1.136.0. I checked Github and my .env file does not contain
IMMICH_MEDIA_LOCATION
IMMICH_MEDIA_LOCATION
so that's not it.
Nothing has changed in my setup in the last months. Watchtower keeps Immich up-to-date, and has been doing so for months without issue.