Great -- thank you for the feedback. Bug logged, ID https://feedbackassistant.apple.com/feedback/9851914

Yeah, definitely not just opendiff. I've seen it periodically in some other tools, but as they were being run from scripts haven't tracked down exactly which tools yet. The bugs are public, but I believe that you need to sign up for a (free) developer account to log in. What are you seeing when you try to visit the link? Per your "went away" comment -- I though that this had gone away from opendiff for a similar reason (updates installed) but now it is back again.