Sometime when you try to save changes on Divi builder page and it shows can't save changes error or in Divi > Theme Options, saving any change just shows the spinning wheel, if you are using WordFence plugin that might be causing this trouble. To confirm is WordFence is creating this trouble for you, just deactivate it and try to save again, if you are able to save, that means WordFence was the trouble maker here.
It can be fixed by following the below process
1. Go to the Wordfence Firewall > All Firewall Options
2. In the “Web Application Firewall Status” change to “Learning Mode”
3. Try to repeat all the actions that were previously getting blocked
4. Go back and change the “Web Application Firewall Status” change to “Enabled and Protecting”
Hope this helps 😄