Here another perhaps helpful
partial remedy during bug-season:
It helps to log out and/or close the session and start a new session.
If I've seen "all cookies cleared" the remedies I mentioned work i.e.
(1) "What's new" and "New Posts" in the topmenus then work if not
(2) Posting works if one logs in via the thread
But as said before: Install the previous version of the forum-software,
least reinstall the version that's now buggedly active seems the best
to try out to get rid of this set of bugs.
The forum-software is by far the likeliest candidate for the cause of