If you happened to run into this issue, it is most likely caused by a problem with the WPBakery Page Builder plugin; this has been confirmed several times with GoDaddy hosting plans and with a few SiteGround hosting users as well. The problem is hosting related, and it is triggered by the mod_security check; it causes this issue when it comes across some more robust and feature-rich themes from ThemeForest.
Luckily, there’s quite a straightforward and simple solution for this.
After the # END WordPress, add the following module to the WordPress .htaccess file:
SubstituteMaxLineLength 10m
After you have done so, you can go ahead and try editing your pages. In the event that the problem persists, replace that line of code with the following code:
#WPBakery Timeout fixer - .htaccess
<ifmodule mod_substitute.c="">
SubstituteMaxLineLength 10M
LimitRequestBody 9999999
</ifmodule>
This should sort out the issue with the SubstituteMaxLineLength, and everything should be working as intended at this point.