Jellyfin not restarting after update of Docker Engine container on Asustor NAS

[Lynd148]

I am new to this forum but have not found reference to this exact problem here.  I have Jellyfin v10.10.6 installed on Asustor AS6702T running ADM version 4.3.3.RC92.  It runs in Docker Engine container.  It has all been running fine for about 3 months, accessed from a variety of peripherals across LAN, including Firefox browser on Windows 10 notebook, Jellyfin media player v 1.12.0 running on Windows 10.
I recently updated Docker Engine from previous to latest version 27.1.1.r5.  The routine warned that Jellyfin would be temporarily stopped and then restarted once Docker update was completed. No one was using the Jellyfin server at the time. Unfortunately end result was that Jellyfin did not restart and apparently would not restart.  I tried various ways to restart including restarting NAS.  Right clicking on the Jellyfin icon on main Asustor screen indicated that no server was running, same from Jellyfin Media player on Windows notebook.  Also tried various browsers that simply ended with blank black screen.

Reinstalling Jellyfin made no difference.  Uninstalling Jellyfin and reinstalling made no difference.  Uninstalling Jellyfin and also deliberately deleting all remaining config and metadata files - and then reinstalling Jellyfin finally yielded a running Jellyfin server.  I then had problems logging on which were likely due to caching problems on browsers (I can see other posts about this). Having finally managed to get the wizard running to create brand new user I was able to set up Jellyfin, reconnect the media libraries and get them all to scan.  As far as I can tell, I am now back to a fully working system - with updated Docker engine.

Question.  Will updating Docker engine container inevitably lead to the need to uninstall and reinstall Jellyfin?  What if anything should I have done to avoid this problem?  Also, some clarity about precisely how to achieve a clean reinstall of Jellyfin (should it be necessary) - with access to the starting wizard - would be really helpful.

I should emphasise that I am back with a fully working system.  The question is simply about how to avoid this hassle if I have to perform another Docker Engine update in future - and in case anyone else has experienced similar problems

[TheDreadPirate]

I'm on plain Ubuntu and Docker engine updates happen without issue.

If, for some reason, your Jellyfin was taking longer than usual to shut down Docker may have killed the container because it was taking too long. That could have corrupted your install.

Frequent backups is my main suggestion. Or backup before updating to Jellyfin/Docker. Shut down Jellyfin before making backups to ensure a good backup.

[Lynd148]

Thank you very much for your prompt response. It would seem that my problem is local to my system. I will shut down Jellyfin before doing any future updates and will do a backup of Docker/Jellyfin before updating as you suggest.
Regarding second part of my question can you point me to any reliable info about exactly what needs to be deleted if for any reason one needs to do a new 'vanilla' installation of Jellyfin?

[TheDreadPirate]

You would simply navigate to where you mounted /config and /cache and delete everything in them. They contain all your permanent Jellyfin data. Then clear your browser cache.

[Lynd148]

Thank you. That is very clear.  I hope I won't need to do this again any time soon. Impression from my recent experiences is that clearing browser cache data is a very important part of this