What I suspect might have happened is that while working several days ago, my five year old decided it would be fun to play with my laptop while sitting on my lap. She toggled off a critical forum setting that split all of the news topics into separate topics from their forum topics. I did not notice this happened and moved on. Only a day or so later did I notice the forums were behaving oddly and dug into it, finding an always-on toggle suddenly turned off.
I think what this did is "re-enable" old posts as unread past the first page of a forum. After I re-merged all those topics, they began behaving as expected again.
All in all, this is nothing more than 6/10 behavior from the kid. Last time she messed with my computer while sitting on my lap, it involved spilling a glass of water and bricking a $1200 Macbook.
I'm calling it a win for the Beauchamp household.