So I had a bit of a break from trying to sort this and came back to it. I’ve looked closely at the animations and I don’t know what I saw before - but now they’re not showing any random rotations. I’ve opened the animations up in Blender and they’re fine in there too??
I’m completely baffled, partly because I’m sure I saw some unusual rotations on the gizmos and partly because if that’s not why it’s doing it I have no clue what is causing it.