The Movie posters are not related to your other issues and if you actually check the entries in the logs that look like this…
GetImageHash - unable to stat url http://image.tmdb.org/t/p/original/bEIjH6GroeWaBkn6o7MVpMNbuyw.jpg
You will find they are all dead links. Something happened to a bunch of artwork at themoviedb a while back (I don’t know when or what) and there seems to be a lot of art that either went MIA or had its url changed. The Kodi db stores urls from this site when it scrapes the show then it caches the prefered images locally (which is what your RPi is currently using) and if you ever lose that local copy it grabs a new one from the url in the db. If the url goes 404 on a poster or fanart Kodi has no method for automatically updating its artwork url list (would be a nice feature though). TV shows are a bit different as episodes are displaying thumbnails normally and if they are not present from the online source Kodi default options allow for them to be automatically generated from your actual files.
What I would recommend would be change content on your movie source/s and set them to none and then click OK. It will ask if you want to remove these files from your library. If you want preserve your watched status you need to say NO. Context menu back over this same source, select set content, and then setup your scraper as it was before and hit OK again. This time it will ask if you want to scan or refresh or something and say yes. This should update all your movies, including their artwork url’s, but preserve watched status. This is assuming your not using NFO files. If you are then they need to be updated with working paths or deleted prior to refreshing your library.