A possibly (quite probably) unrelated data point:
Last night (about 13 hours ago), my "Latest" list suddenly was full of closed topics.
I refreshed the page and the same old topics came up again.
Intrigued, I opened one topic, specifically New forum onlin, and saw that it had been closed back in 2021.
I couldn't make heads nor tails of it last night, but in light of this topic I just looked at it again. I searched through my history list (which is how I found the topic above) and noticed something odd in the preceding URLs and managed to reproduce what I'd seen.
In the light of day, what I'd done was now obvious: the "Latest" list was sorted in ascending order (see the ^ to the right of the "Activity" column). I clicked on "Activity" to change the sort back to the default descending date sort, and everything went back to normal.
How this would manifest in 2024 posts suddenly appearing in the "New" list is not obvious to me. But I thought I'd throw it out there and see if it sparks an idea in someone else's brain.