Ian...
uneven development is what I was thinking, but when I took out the roll, it wasn't sticking to anything. It's across the entire roll too by the way, not just this one frame. In fact there's frames that are way worse than this. I scanned this one as it was the least effected, so I thought it would be salvageable. I was thinking it might be something to do with how the film was stored (in a freezer) and moisture?