As reported by @asottile-sentry, upgrading from Python 3.9 to Python 3.10 caused new groups to be made where none should have been. The culprit turns out to be that Python changed timeout errors from appearing as timeout to appearing as TimeoutError. (Apparently socket.timeout and TimeoutError are aliases, and which alias is getting used was changed.)

Though this is the only report of this problem we've gotten so far, we should investigate if there are any other known examples, either from Python or anywhere else.