if you have two versions for the same episode (which happens when you rename a folder), plex will attempt to play the unavailable version (whichever came first) and fails.
Request: Plex should automatically skip or play the next available version. This should be a bug, but it’s been 5 years, and this was never fixed.
I suppose what you’re asking for is the same suggestion discussed in this existing thread:
If so, I suggest you comment/vote in that thread in order to help us avoid distracting or cannibalizing votes (in which case I’ll close this thread as a duplicate).