I've noticed this phenomenon for at least a month now. If I make a post in a thread, it will not show up in "New Posts" until someone else posts in that particular thread. I figured that's just how it was supposed to work. If I made the post, it wouldn't be new to me. If I want to see it, I'd have to go to the particular forum to find it. It would seem simpler though if the platform didn't make a distinction on whether it was myself or someone else who made a "New Post," but I guess I've gotten used to the wrinkle.