Turns out there's some extremely specific weirdness with docker on ZFS. I had to install a userspace FS overlay or something.
But even after all that, I pretty much never use the damn thing. The web interface is the slowest, most bloated and broken thing I've ever had the misfortune to interact with. The desktop and mobile apps have the absolute bare minimum features, and still somehow manage to be broken and unusable.
It sure sounds like a cool idea to glom together your files and email and jira and calendar and everything else into one unified dashboard for your life. But it takes nearly a minute for the web ui to respond to anything. Browsing files takes minutes. And absolutely forget about music or photos, that barely works at all.
At this point, I just use it as a place to blindly dump all my files. I get a notification every. Single. Day. that my backup succeeded, so my files are probably safe I guess. Can't turn off the notification, or filter notifications in general. So I have an unending torrent of useless garbage notifications that perfectly hide any truly important notices.
As much as I want to like it, it's just bad.
Later on, when I set up an old dell xeon workstation as a home server (using proxmox), I used the turnkey image of nextcloud, and have (knock on wood) not had any issues at all.
Anyway - I wanted to ensure it was fully virtualized this next time if/when this happens again. I have it backing up the base vm once a week (I have the file storage separate/outside of the vm). So... hopefully this doesn't happen again to the degree that it did.
Anecdotal evidence tho. Results vary. I like nextcloud because worst case all a wipe would cost me is a re-upload of my local folders over a couple of hours.
Docker monoculture and it's consequences.
"Use the Docker image. It just works!"
Until it doesn't.
I know this will sound very greybeard, but as sysadmins, we can slog through understanding the systems we are running when we set them up, or we can wait until they break to figure them out. You can tell which path a sysadmin chose when they things like, "I upgraded and my containers wouldn't start, so I gave up." Why wouldn't they start? What's in the error logs?