plexbmc – no preview video files

Hi all,
recently i installed plex server on my windows 10 pc and installed the plexbmc addon on my raspberry pi (librelec-kodi krypton) and on my other windows 10 pc (kdoi krypton).
All is working; i see my media files and can browse them, the only thing that i can’t see is a preview image when browsing media files (see attached screenshot). This is the same for the plexbmc addon on my windows pc and on my raspberry pi system. I tried to change the skin but that only results in a different icon instead of a preview image. When i browse with a different device to plex.tv/web the video preview image is ok. Also in my plex server the video preview image is showing so i’m guessing it’s a kodi setting or a addon setting that i’m overlooking. Thx