The resonant bit for me was movies. If characters are sufficiently visually different, I'm fine. But if it's a movie about a bunch of similar people, I'm screwed. Tinker Tailor Soldier Spy was about a bunch of middle-aged English dudes all dressed as British civil servants. At some point I just gave up.
Yes - this sort of thing. I find it especially difficult with e.g. TV series where the main actress changes her hair halfway through - I almost always need to ask if it’s the same person.
In “Orphan Black”, It wasn’t until very far in that I realised Rachel was also a clone; without the narrative clue, I just had no idea.