Yes, this is a known thing: Raise the rep bar on late answers
The short answer is we recently expanded the pool of people eligible for having their late answers added to that queue. It was very effective in terms of adding more review tasks because it wasn't time limited. All eligible answers going back to the start of the site got added a few days ago, ...
My guess is that something was changed in the algorithm to determine what constitutes a late answer. Especially since many of the "late" answers were given years ago.
I've cleared the queue in the mean time, but it didn't seem like anything to worry about.