TV Episode Metadata

@golfguy0082 said:
My last ditch effort to get this to work was to use a tool called Mp3Tag to manually update the metadata to match the filenames (previously the metadata was blank). Although this now works, it’s a pain to have to update the metadata for each file.

It is easier to just erase the metadata from the mp4 file.
mp3tag allows you to do that for several files at once
and to re-‘optimize the mp4 files for streaming’ afterwards (it is in the right-click menu)

Are there any log files that might give me a clue as to why Plex is getting confused in the first place?

You can instruct Plex to give the title from the online databases priority over those awful embedded ones:
Settings - Server - Agents - Shows - TheTVDB
In there, grab the line ‘Local Media Assets’ with your mouse and drag it downwards, so it ends up being at the bottom of the stack of active agents.