Hi There @RSMG
Thanks for writing in! I'm sorry to hear that you're experiencing this issue. Most probably you're running out of your allocated memory on your server. First make sure that you're fully updated by referring to our version information here. Then once you updated your Pro theme, you need to clear style cache by head over to Pro -> Settings page. Also if you're using a caching plugin, you need to purge server cache as well.
If you're still having issues, then please check with the following as well.
Please install the following plugin (https://wordpress.org/plugins/wp-serverinfo/) activate it and then head over to Dashboard -> WP-Serverinfo section. Then check the following server configurations.
PHP Version - We recommend PHP v5.6.x or higher to avoid incompatibility issues. Some hosts allows to switch PHP versions within the hosting control panel. If not, you can contact your hosting provider and ask them to update.
PHP Memory Limit - We recommend PHP memory limit of 512 MiB. You can follow our guide here. Please check to see from WP-Serverinfo page whether it has been increased. Some hosting providers does not allow to increase it manually, so you will have to contact them directly.
PHP max script execution time - We recommend the value of 120 or higher (300). Here's how to increase that value (https://www.simplified.guide/php/increase-max-execution-time).
Also follow our troubleshooting guide here (https://theme.co/apex/forum/t/troubleshooting-builder-preview-warnings/14404).
If you're still experiencing this issue, please provide us with your WordPress login credentials along with your FTP credentials in a secure note to check your issue further.
Let us know how it goes.