I was collecting general FRN errors in the past and although I switched to star note errors, this is still my favorite. Instead of a previous sheet being tilted, folded, or bent when being printed I believe one of the previous sheets to the one below had a hole in it. I can't explain anything else. Opinions welcome.
You hit the nail on the head. However these usually occur with strait edges on the transfer. Like a diagonal, or horizontal, or vertical. This one is unusual in its appearance (shape).
One of only two error notes I have in my posession: a funny error! It looks like a loaf of bread or beard.