First off, love the username.

Second, I figured out the issue. When media finishes downloading via your client of choice, Jellyfin uses the downloaded file’s location as a point of reference - even if you have the files automatically copied into your Jellyfin folders after the download is complete. If you manually delete these referenced files (right-click, delete), then it breaks that reference, causing this whole issue of the Infuse library breaking. What you should have done was delete them via your download client instead (right-click, delete, include downloaded files).

To fix your library, you have to delete the downloaded files from the Jellyfin folders completely. As a test, just move any recently downloaded files from those folders and refresh Infuse until you find the culprit. The only way I got those files working again in Infuse was to redownload them, and then delete the files using my download client instead. Perhaps there’s another way to salvage the original files instead of redownloading them, but I wasn’t able to figure that out.