The spoiler issue has existed for many years from even before Plex introduced live TV or DVR as the same thing happens for imported shows for other sources as well as for content captured by Plex.
It has been requested that the captured frame(s) be chosen from early in the video or even that the position be user selectable. Plex has chosen to exercise their “selective inattention” and has managed to totally ignore their users. This, and many other issues, are just continuing examples of Plex’s lack of any concern for user friendliness.
Plex is unconcerned about their product doing anything except what Plex wants it to do. Plex only sees users when they look down to see what they are stepping in.
Plex has become more fluff than substance and this is reflected in things like this where they cannot even get the little easy things right.
Plex is on the same level as golf which Mark Twain described as “A good walk, ruined.” Plex is good (even great) software, ruined.