I noticed on a couple of days ago that some (not all) of my collections are broken. The collections are showing, with zero movies, and the movies themselves are showing in the library and are missing their collection tags (and the tags for the broken collections are missing). This shows the same on the server (running version 1.20.1.3252), Windows client (latest version) and Android client (also latest version). Everything was fine last time I used the movie library about a week ago, and I’ve changed nothing since then.
Not aware of a general issue.
I’ve noticed in the past that users run into issues if they have automatic / scheduled library updates enabled and the external drive gets disconnected or takes too long to spin up. If you have “Automatically empty trash after scans” enabled, this will result in an impacted library item to be dropped. If the movie is added again during a subsequent scan, all manual additions (e.g. collection tags) will no longer be on that item.
If you have such a situation, I strongly recommend to disable “automatically empty trash after scans” (in your server settings: Settings > [Server Name] > Library).