I’ve been having this very same issue for almost a year (see this post Problem downloading artwork from TMDB (Argentina Users))
Apparently there is a problem between Plex, TMDB and Cloudfare, that’s why TV Shows works fine, because it’s pulling data from a different database.
Some people claim that when their ISP changed their modem/router, the problem got solved.
In my case, I know for a fact that is an ISP related issue because when I connected the PMS with a 4G LTE connection, it pulled metadata as it should.
It is beyond my understanding why no one could get this problem fixed.
