I think tom80H nailed it. I suspect you had the numbering wrong for the episode, added them to Plex (who combined them), then renamed the file after. You can try the “Split Apart” option, but it’s show level, and will split the show into two entries (I think). Plex Dance the entire show (or just the affected episodes) to fix this.
Renaming files in-place after Plex has seen them causes many issues. It’s best to Plex Dance the files afterwards, just in case.
