I have a few of those in my debug.log
[24-Oct-2018 09:12:12 UTC] WordPress database error Duplicate entry '0-d551e28a17779d2-4-19' for key 'unique_tracking' for query INSERT INTO `wp_wpforo_visits` (`ip`, `time`, `topicid`, `forumid`) VALUES( 'd551e28a17779d2', '1540372332', 19, 4 ) made by require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('wp_loaded'), WP_Hook->do_action, WP_Hook->apply_filters, wpforo_logs, wpForoLogs->visit, wpForoLogs->add_visit
Any ideas ?
Please navigate to Dashboard > Forums > Tools > Debug Tab admin page, leave us the screenshots of wp_wpforo_visits table ( [Tables] subtab).
Also please provide us the Server Information as well ( Dashboard > Forums > Tools > Debug Tab > [Server] subtab) .
Sorry for the bleeding of the previous spost. I can't find any other way. Edit it as you wish ....
There is no problem with tables. Somehow you got different db errors which are not discovered in other websites. Maybe you do non regular tests or some specific processes are going on your website. The same wpForo is installed here and used very actively we don't see such error. So I'm sorry but we have no idea.
We'll take a look on this if we got more examples and cases. Thank you for letting us know.