If you happen to have an installation with a large amount of Users (regardless of whether or not they use it or not), expect the container to take a while to go from 'Starting' to 'Running' when you boot it for the first time after updating.

This is because Nextcloud is attempting to generate a bunch of avatars for some reason, as part of the new update. To give you an idea, it was probably taking 5-10 seconds per user for me. I was confused at first, and so I restored from backups a ton of times. You don't need to do that. Instead, just give it the time to run through it's process and it will go to 'Running' just fine.

Anyways, here's where I got the information from, after experiencing it myself: Thread on Nextcloud Forums

Also, as a note, if anybody is having trouble with add-ons after an update, sometimes, the problem can be resolved by uninstalling the disabled add-on (after the update), and then re-installing it. For some reason, that seems to get it working again (whereas just re-enabling it will not). Every time I've done it, it keeps the configuration settings for the add-ons just fine, although it may be good to manually take a screenshot of those addon settings before doing the removal, just in case.