I thought this was happening yesterday but I could not keep up because so much going on in threads I was following. However, this morning I had 21 new comments in threads (shown with the pink envelope icon in top right). I clicked on 3 of them (that took me to the threads) and then used the Dismiss All button to clear other messages from same thread, and they all went away. About an hour later I refreshed by Chrome and it said I had 18 new comments (the 18 I did not click on). I checked and they were not new, all ones I had seen before. I clicked on Dismiss All again, and go no response from the button. Could be me using it wrong, but wanted to toss it out there encase I am not the only one noticing it.