Plex doesn't put the right covers and images

Hi,
first of all, sorry for my english, i'm french

So, i'm using Plex since a while and i didn't have this problem before
Yesterday i downloaded a few movies from a website i never used before and with those movies (and those movies only), Plex doesn't put the right covers and no informations about the movie.
I guess some meta-data are missing but i don't know how to fix that.
could you please help me?

Thanks ;)