Similar issues for me where I've read all the new posts in a lengthy thread such as this one, then decide to go back and reply to a specific post
As I've already read the posts, clicking Jump To New doesn't work.
So I have to click through the pages to find what I want which may be somewhere close to the end of the thread.
Now if I could choose Newest at the top (as used to be possible), it would be MUCH faster.
As it is, despite the many significant advantages of the new software, its taking me longer to navigate the site than before