There is the trick of placing the “Local Media Assets (movies)” completely down,
but then the movie cover placed in the same folder will also be ignored.
Reference: Picture on Cast actors not showing
However, it appears that in the MP4 file can be a list of actors that could cause this.
So as a test, I deleted ALL MP4 metadata (using Mp3tag), but that didn’t seem to fix it.
But then I took an extra step:
I “Unmatched” the movie and ten “Fix match” the movie and THAT seemed to fix the issue.
–> CORRECTION: Doesn’t seem to work for all movies … ??? Not sure what is going on here.
