Naming of films changes after metadata download

Yep - almost always - but here’s the cure (as you describe):

Drag and Drop - move LMA to the bottom of the Active Agents under ALL tabs in Shows and Movies. Red: Where it was. Green: Where it goes.

Refresh Metadata at the Show Level should fix things after that, but if not, The Plex Dance will:

Public Enemy #1 remains file naming and structuring, but the WRONG default position for LMA is, without a doubt, Public Enemy #2, if you happen to be an MP4/M4V user/victim.