That’s odd, it works for me.
I'll post if I continue to notice it.Us as well.
At the moment for some threads it takes me to the first post of the first page, others to the newest unread post. In both situations, there are unread posts. (The button that @PinkLucy shows does take me to the newest unread post either way, but that still introduces a new 'step' to read threads that wasn't necessary before.)