Since I updated to 2.8 my site has fallen over at least once a day. MySQL queries go out of control and the site grinds to a quick stop. The only way to get it back up again is by restarting MqSQL. Is this a known issue!?
There is no such known issue.
Please install
https://wordpress.org/plugins/query-monitor/ plugin on your site to monitor the sql queries.
Also provide us the php error log of your site, upload it somewhere and provide us the link here.
Thanks. What error logs do you need specifically? Apache? MySQL? Does WPLMS log anything?
Well we need your server php error log .
Also please make sure tha envato market plugin is disabled in your site . If its activate then please deactivate it .
Please also repair and optimize your mysql tables from php myadmin .refer : https://www.a2hosting.in/kb/cpanel/cpanel-database-features/optimizing-and-repairing-mysql-databases-with-phpmyadmin
Please install https://wordpress.org/plugins/query-monitor/ plugin on your site to monitor the sql queries.
Try deactivating third party plugins .