I don’t know for you, but compared to the old forum and many other forums, the Elektronaut forum is very slow. It needs longer time to load pages, and this makes the browsing not smooth.
In the old version, the way the site handled the visited topics was by far more efficient. Here, it seems that the only mean to tag a thread as read is to click on “Scroll to first unread” (which is also triggering a slow reaction).