Updating failed. The response is not a valid JSON response

We have a Beaver Builder website for a client and all of a sudden anytime a pages is edited using Beaver builder, it shows the following error:
Updating failed. The response is not a valid JSON response. Then it gives me the option to leave the page or cancel. If I click Leave the page then I am able to edit the page sometimes or I have to hard refresh the page and then I can edit sometimes (sometimes I can edit and save and other times I am unable to edit any module, just nothing happens when I try to edit any module). Previously I was also unable to edit as it was giving me a 403, but adding define( ‘FL_BUILDER_MODSEC_FIX’, true ); resolved that issue.

What’s interesting is this started happening when I installed Wordpress Toolkit on the hosting account. But when I removed Wordpress Toolkit and restores the website from earlier the issue was still present. Then I reinstalled Wordpress Toolkit and cloned this exact website to a subdomain. Now the cloned website does NOT produce the error. But if I clone the subdomain website back to the main website, the issue still persists for the main website.

If I got to the pages area and mouseover any page and click the builder link for that page, then I am taking to the builder without the json error.

Website is using Beaver builder Version
The child theme says Version: 1.1 (template: bb-theme)
The parent theme says Beaver Builder Theme Version: 1.7.9

One thing to add is this all started happening when the Cpanel Wordpress Toolkit was implemented on the domain. And strangely enough, when we clone the main website with the issue to a subdomain, the issue then no longer appears.

Your help would be most appreciated!

I have no experience with cPanel or the cPanel WordPress Toolkit or what it does. I recommend disabling all plugins except for Beaver Builder and remove any custom code you may have added and see if the issue persists.

If it does, please submit a support ticket.

Thanks for your input. We tried everything you suggested but it did not resolve the issue. So we simply copied all the files to a new identical cpanel account and it resolved the issue.