It almost looks like a light leak from taking the empty canister out of the changing bag when getting ready to work on the second reel. That's my first impression. It is clear though - one on the front of the cat and two in front of the back leg of the cat; that makes me think it could be the cut off leader in addition to a light leak that caused it. That would imply technique in my opinion. But testing in controlled, step by step, room lights on, room light off-type procedures would be needed. If you cut the leader off, and had to take your hands out of the changing bag for something, that could explain one possible light leak. Just trying to throw ideas out here to be considered.
I suppose your changing bag could be going bad too. Was it washed in with some kind of detergent?