Yes it’s not always 0, although the new message seemed to be right on target to delete the very-old-version.
I’m not sure if my little test would have had more than one dblock to send, and I don’t know what it’s thinking.
This report got this error with a 5GB dblock-size and involved trying to get the backup stopped. I don’t know whether there’s also a test case that could be made on that. Throttling might allow test with a smaller dblock.