We figured out what the problem is, there was an issue while we moved to TVDB. For a short period of time we were using a wrong url to download missing images.
The issue was fixed very soon but if you ran update library during the broken build it populated your file system with invalid images for series/episodes that didn’t have any actually images.
The issue is already fix however we are going to release a new update to do clean up of these “images” so they should automatically disappear in a day or so,
the reason you don’t see images being downloaded is because the episodes/shows that had these files didn’t have images and were originally downloaded by mistake.