Assuming the library is set for "Shows" or "Mixed Movies and Shows" (so Jellyfin doesn't assume it's a movie), I would make sure you are following the correct folder paths.
Show name -----> Season 01 -----> Episodes S01E01
If you had moved it around a lot, sometimes Jellyfin ties that folder to being a movie, so removing it from Jellyfin and placing it in a new folder and deleting the old folder has sometimes helped me. Beyond that, I don't know what your configuration is so I'm just guessing.
I complain about Jellyfin a lot and have no idea what I'm doing.
