I may have found an unofficial work around for the loss of the first unread post. It seems that the coding behind the forum pages has retained some of the coding for that.
On the forum pages which list the topics for that forum look at any topic which you have read before but has since had new posts.
DO NOT CLICK ON LAST REPLY. Instead right click on the last reply and select Copy Link Location.
Paste that into the browser address bar.
From the right delete the text referring to last reply back to the = but not the = itself.
Then add after the = unread (so =unread)
Then press return for the browser to go ahead.
And it seems that you go to the first unread post.
No guarantee that this will always work and of course I hope that the first unread post link returns in the future.
Of course if there's only one post since you last read the topic it would just go to the last post anyway so there needs to be more than one new posting to see this.