General Discussions.
I scroll down the list a bit and look at some topics. This one here shows up in my list with the info that the last post was 23d ago:
As can be seen, the last post was in September 2023, over a year ago.
I checked the topics directly above and below in my list, they are fine with last posts really being 23 / 24 days ago.
Maybe someone posted a message, then realizing the age of the thread or for some other reason, deleted it.
So the system remembers the last activity 23 days ago, even though that message no longer exists.