More of an FYI. Had been running Seafile on Server 2016 for a while now and recently it stopped working. Saw KB5021235 was installed overnight and that all of the containers on the virtual hard disk were suddenly gone! Very important to backup that virtual disk otherwise you will be re-building your entire seafile setup. It’s not just building the containers either as there doesn’t seem a way for newly spun up containers to reference the existing seafile data. You will have to re-build everything and re-sync all files from one of the clients. If you have a backup of the virtual disk you can just restore that post-update and everything will work again.
Just as a follow-up, it seems if you roll back KB5021235 the old containers do come back meaning this update seems to do something odd with the data on the virtual hard disk.