I've had intermittent issues where if I've clicked on "mark all as read" in a subsection eg Wanted, not all of them are cleared. Majority of the time, it sorts itself out. Over the last 24 hours, it has been more persistent and the same threads will not clear - even if you click on NEW (next to thread title).
EDIT: And I've now just had the "Please try again. If you come back to this error screen, report the error to an administrator." message when posting, only to reload the screen and find it posted.