Thanks for providing more details.
I see that both sites are virtually identical except for the fact that X and Cornerstone is up to date in the site that is not working. I’ve updated the other site that is working and now it’s not working.
I remember the previous site I checked was not yet updated yet the issue happened though so this is really weird. Honestly, this only means that the web host is unstable. The web host usage limit or an unknown configuration is the only thing that varies in the setup. Our products and WordPress in general only executes code. If the server could not handle the execution of all the sites in their server, there would be problems like this.
By limitation, I’m not referring to memory only but also CPU usage. That’s especially the case if you have many sites in a shared host where usage of other users or even your other sites can affect the rest of your other sites. If you’re in a VPS, it’s most probably some server configuration especially security configuration.
Regretfully, we’re out of options in this case. We also could not dig deeper into this because we do not have direct access to the server. By direct access, I mean server controls and not only FTP or cPanel.
Personally, I’ve never experienced this issue yet in any of my test sites. To quickly check my claim that the web host is unstable, please try setting up a fresh WordPress, X and Cornerstone install in another web host. I personally have tried cheap hosts like FastComet and NameCheap hosting. Just note that it’s not a recommendation but just to give you an idea. If you could test quality managed hosts, that would be even better.
I also forgot to tell that please disregard this error PHP Fatal error: Uncaught Error: Call to undefined function mysql_connect() in /home/design45/brevityocr.designbythinkdev.co.za/wp-includes/wp-db.php:1643
. It’s a past error and if that still applies, your site should have been down as it’s a Fatal error and it relates to database connection. It’s not related to the issue at hand.
Thanks.