MP4 files?
Move Local Media Assets to the bottom of the stack of active agents under all tabs in Shows and Movies:
Red: where it was
Green: where it goes
Then, if as you indicate, your show, seasons and episodes are in perfect order… Refresh Metadata - or Plex Dance if being stubborn:
If you’re not using MP4 files - maybe a Plex Dance is all you need. Check Show/TVDB for precise naming and structuring before The Dance.
The contents of this guide - are NOT just suggestions:
https://support.plex.tv/articles/categories/your-media/naming-and-organizing-tv-shows/
they are, in fact, requirements… just sayin’.
Also:
Edit the Show or Library and make sure Airing Order is set in the Advanced area. DVD Ordering would really mess things up at this point. Unless that’s what you want - and you don’t.