My apologies – I’m a moron and hadn’t uploaded any images into those galleries. The moment there were images in them, they displayed fine!
Did you find a solution? I’ve got 4 galleries. 1 works, the rest do not. Everything seems to be set the same for all of them!
Are you, by any chance, trying to put more than one gallery on a page? I don’t see why that would be a problem but that’s what I’m doing and I wonder if it’s the cause.