One season in certain shows becomes "the entire series"

[TH35]

Just wait for v10.9.5, this bug will be fixed then. You'll then be able to continue naming the folders like you are now.

There were recent changes to how Jellyfin handles metadata in v10.9, and this is one of the bugs that slipped by.

Thank you. For anyone else reading, I can confirm that I have downgraded to 10.9.3 for the time being and done a refresh on an affected series, and it resolved the issue for now.