Soldato
I've noticed with some threads when I click the envelope it takes me to the first post instead of the last read. It looks to be related to how long ago it was posted on. The Diablo 4 thread in PC Games did it just now. Last post was 31st March. New post in the early hours of the morning and it took me to the first post.
I think this is caused by data not importing correctly during the forum changeover or maybe post ids changed or something like that.
I get the same problem on any threads where I last read them before the changeover. Any threads which I've read after the new forum went live work correctly. So it'll eventually fix itself as after a while there wont be any threads left which were last read pre-update.