Please navigate to Dashboard > Forums > Settings > Feature admin page, make sure the HTML Cache is disabled. Then navigate to Dashboard > Forums > Dashboard admin page, click on [Delete all caches] button. If you use some other cache plugins, delete those plugins caches as well and press CTRL+F5 (twice) on the current page.
It seems I found the solution. Hope it will help other people.
Yes, this was a database problem. If you have access to phpMyAdmin then login to it.
- Select all tables of your WP installation.
- Choose in tables actions - Check tables.
- Select all tables of your WP installation again.
- Choose in tables actions - Optimize tables.
Now the problem has gone!
We found this is not wpForo issue. This is a bug of MySQL 5.6 version.To show pagination it should count the total number of posts, but count(*) on InnoDB tables sometimes returns 0. This bug was reported to MySQL community on 11 Apr 2016. You can see the discussion here: https://bugs.mysql.com/bug.php?id=81031
So the solution is contacting to hosting support and asking them to update MySQL Server to 5.7 version. Or try to change wp_wpforo_posts table to MyISAM engine (not recommended).