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:
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
This should sort out the issue with the SubstituteMaxLineLength, and everything should be working as intended at this point.