SOLVED: I fixed everything, sort of...

[Randall Stevenson]

After realizing how badly I mucked up my Jellyfin Server, I went drastic and uninstalled everything Jellyfin.  After installing 10.10.6 fresh and new (only added plug-in being TMDB Boxed Sets), I see that I fixed my previous issues, filtering by year can count up to 2024 now, no more cursed collections, library scans actually complete without failing. But now I have a new oddity, every movie that belongs in a collection are both in their proper collections and in the Movies library.

[theguymadmax]

You have the option to display collections in your Movie Library. To turn this off, go to Dashboard -> Libraries -> Display, and unselect "Group movies into collections."

[Randall Stevenson]

Forgot about that setting, I ticked it and now everything looks correct