No it's due to nextclouds crazy AIO container that creates other containers automatically, and hides the entire process from the user so there's no easy way to diagnose issues.

We can't turn on web server logging? PHP logging? We don't take DB backups? We can't revert to the previous image version? The crazy AIO NextCloud Docker image doesn't store your documents as plain files in a data/{$USER}/ directory that one can always rescue?

"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?

No, it‘s their insane composition of „not-what-docker-was-made-for“ architecture. Their all in one solution is a bastardized version of compose, just give me a compose file with all services you run.