Curious why this happens and how can I avoid it.

I've been filling out cast lists and primary images for the show World's Most Evil Killers https://www.imdb.com/title/tt15802630/?ref_=ttep_ep5 I've had this happened several times.... When I know who the actor is in the reenactment scenes I like to add a screen shot so they have it on their own name page galleries. However when I add a screen shot to the episode the following happens.... The image or at least the first one if there is more than one, appears as the primary image under the episodes list for that season... but it doesn't appear as the primary image on the episode page.... nor does it appear as the primary image at the bottom of the page for recently reviewed...  I don't want the screen shot to appear as the primary image anywhere. And when I go to the production still supplied by the production company to change it back to the primary image it doesn't give me the option. This has happened three times in this season https://www.imdb.com/title/tt8888656/episodes?season=6  I know this is a glitch in the Matrix but would be nice to avoid this and have the season (series in the UK) list of episodes look consistent.    Thanks.