I have not seen any info from Plex with a specific list of movies, etc. that are affected.
The only way I know to check it to edit the movie and choose Poster. If you do not see any, then it is affected.
I’ve these movies & they’re all affected:
- Rambo movies (First Blood, etc).
- The Dirty Dozen (1967)
- My Fair Lady (1964)
- Once Upon a Time in the West (1968)
- Notorious (1946)
Additional movies listed in this thread: Missing movie artwork
