Help? TV show posters keep disappearing.

If there is another place I should post this, please tell me.

Normally, I open Plex (on Roku) on my TV and go to TV Shows, and see all my shows with their “posters”. When I go into a TV show, I would see the thumbnails for all individual episodes. These come from TVDB. Some time ago the thumbnails were replaced with that season’s “poster.” The thumbnail is there If I open an individual episode, along with the episode description, and the episode plays fine. The thumbnail is just not there in the grid/list of episodes. (Is there a way to get that back? If not, I can live with it, but that is not my main issue.)

The main issue is that the “posters” went away too. When I opened Plex, there was the gray box with the X in it where the posters used to be, for all TV shows. Opening a TV show, nothing but the gray X boxes. Opening an individual episode shows a gray box (without the X) where the episode thumbnail would have been.

I followed the steps to re-set Plex and the posters came back. (The ep thumbnails are still replaced with the season poster so fixing that must be another thing.)

It worked fine for a few weeks, and then the posters disappeared again. I re-set Plex again. It worked fine again for a few weeks. Now the problem is back. It’s not a huge deal to re-start Plex, except that it erases “watched/unwatched” status and my star ratings, and that is a pain. Also, it’s a chore and takes time, and I would like to avoid having to do it every few weeks.

What do you think is going on? I had no problems at all for years, and now this is turning into a regular thing. Please tell me if I need to provide any other information, or if I am not clear what I am talking about (it is kind of hard to describe.) Many, many thanks for any help.

Edit: Hang on, it’s not an X. It’s a line drawing of a TV set in the gray box. I took photos & will attach once I figure out how. (I should add that if I open Plex on my PC, all posters and episode thumbnails are always right there where they should be. The problem is only on my TV.)