Images for tv shows not showing on watchlist

As an example, for the crown. there is an image but if i add episode 5.1 to my watchlist there is just a place holder https://www.imdb.com/title/tt11709728/?ref_=wl_li_tt Image can be seen here, but not if i add this episode to my watchlist. movies are fine  Happy valley 3.1 is another example https://www.imdb.com/title/tt6779064/?ref_=wl_li_tt the images dont show when you view your watch list