A lot of TV Show posters have changed to foreign language or just simple disappeared.
Thanks for reporting. For me this has resolved with a few exceptions, can you confirm?
Collected this issue and its status in an overview post: [TheTVDB] Issues with missing episodes, images, adding shows
Thanks for the response. The posters are displaying now, but still not the right ones. It doesn’t show the most voted, best posters. Almost every poster has changed compared to last week.
Note: There also was an issue where the SeriesGuide poster caching server did not allow the new subdomain used by TheTVDB for image URLs (https://artworks.thetvdb.com). I added it to the whitelist.
But this should not have affected existing posters. At least in my testing TheTVDB servers do not redirect image requests to this new subdomain, despite their forums saying otherwise.