Could be a few things. Some movies have junky tags on them that shouldn’t be there.
Otto made a howto for mkv tag fixing.
It could be that you just need to Empty Trash, Clean Bundles, and Optimize DB.
Then maybe Plex Dance a few folders and see how it goes.
Those things work in conjunction with the Local Media Assets agent that people tend to put first on their list to deal with local art/subs.
What triggers a library scan? What server version do you have?
http://IP:32400/identity
