Server Version#: 1.26.0.5715
I have this issue on the image?

and it is only series, not all?
some series plays fine others don’t
Server Version#: 1.26.0.5715
I have this issue on the image?

and it is only series, not all?
some series plays fine others don’t
Click into the season, to see if only some episodes are affected.
Look at the Plex media info of these episodes, to see if there is only one file or several files connected to the episode poster. If there are several, only one of them might be missing.
“Scan Library Files”, followed by Empty library trash is supposed to clean this status.
(Unless you have an empty or unavailable folder added to your library.)
Check all your media file storage locations for presence and accessibility before doing this!