plex_sync.py: Mismatching media on source and target server

[Casvt]

In which file is the bug?
plex_sync.py

Describe the setup (arguments and their values, how it was run, etc.):
Any setup that requires matching media on the source server to the target server. aka finding the ratingkey of the media on the target server.

Describe what the bug is:
Matching the media sometimes leads to a mismatch. With season posters, sometimes season x posters from other series are "matched". Or episodes of series aren't sync in watched status because they weren't found on target (even though it was there).

Describe what should be happening:
The matching should happen correctly or the media should be skipped but not mismatching and continuing.