The "first unread post" feature has never worked properly on this forum, nor on this forum's competitor and compatriot, the Sudoku Solvers forum.
Thus, it appears to be an issue with the specific version of phpBB used by both of these forums. There is probably nothing that the managers of either of these forums can do about it, without help from the creators of phpBB.
"First unread post" seems to work only if there are 16 or more posts (i.e. 2 or more pages of posts) in the topic. If there are 15 or fewer posts (i.e. just one page), it just jumps back to the previous page, where the user had just come from to begin with.
I'm not sure what happens if there are 16 or more posts, but the "first unread" happens to be in the first 15.
On the U.S. Chess forums (
www.uschess.org/forums), the feature works properly. They actually use an older version of phpBB. Nicer colors, too -- I don't know whether that's due to the version being older, or because of something U.S. Chess did when they set up their forums.
Unfortunately, you won't be able to test the feature on U.S. Chess unless you are a member of U.S. Chess, which costs about $46 per year depending on the options you choose. You can, however, browse that site and read the forums, but you cannot make posts, nor use the "first unread" feature, without becoming a member.
Bill Smythe
"Read first unread post" shown left to the topic title when displaying the list of the topics, is too small and difficult to click on mobile devices.