There was a bug that did mess up the posters. The latest PMS fixes the bug. Unfortunately, the damage caused by the bug cannot be fixed so the poster will not “just come back”. You will need to refresh your library. If you have blank posters showing in the edit poster window, then those are stuck there. You will need to do a Plex Dance of the affected artist/albums. For some of you, like @blackzwe, recreating the library may be easier.
