I just finished adding my Stargate SG-1 files using thetvdb.com naming for the files using the naming format recommended by plex, now season one episodes 10-19 are no longer showing up. They were showing fine but as I finished adding season 10 those episodes stopped showing up. I have identical file structure for all 10 seasons. I am now adding my Sharpe collection and only the first 6 movies are showing up.
looks like I answered it myself. To fix the problem I renamed the season file from Season 01 to season 1 then renamed it back to Season 01 and it registered the files again. Renaming the season files in my Sharpe directory also fixed the problem with those not showing up.
Another option - this works for me.
I have ALL episodes in one folder.
Plex still shows them as season 1-10 and all works !!