Was that near one of the walls? In that case, it's because of the camera's collider which I honestly didn't even spend much time testing at all... but I'll keep it in mind!
Possibly! I was too busy trying to get run over that I didn't pay too much attention xD ahaha. But if I recall, I think at times I was in the middle of the road and it would start shifting to the left (or right) even though I was standing still.