I've seen streaming services spoil an episode with just the thumbnail. I can't remember what show's twist was ruined for me, but I'm pretty sure it was Netflix.
Netflix also has a really annoying habit of re-ordering seasons. For some bizarre reason shows like bake off are listed with the most recently added series first. For some shows that might not be a huge problem but in the first episode of one series they actually recap the winners of all previous series, spoiling several years of programing for unwary netflix viewers.
At least one extremely typical problem on Netflix and basically every other streaming service is that the episode thumbnails (which I usually have to go take a look at just to find out how many episodes there are) will ruin any cliffhangers. If a character's survival seems uncertain, the uncertainty will be lessened quite a bit by seeing their face in the thumbnail of a subsequent episode.
Netflix also has a really annoying habit of re-ordering seasons. For some bizarre reason shows like bake off are listed with the most recently added series first. For some shows that might not be a huge problem but in the first episode of one series they actually recap the winners of all previous series, spoiling several years of programing for unwary netflix viewers.