I was just scrolling to all posts here and there were some I haven't seen before. Happens often. Is it the design of smth else?

Indeed, I can see upvotes, now. Well done.
As for posts, yeah... happens to me, too. Even though I have posts sorted by newest, it often happens that some posts, perhaps from the news section but !necessarily, tend to get inserted in-between the ones I've already read.