Recently faced this issue on one of the website hosted on octodomains.com.au hosting. If mod_security rules are enabled, the Divi Editor does not work for homepage. The rules are enabled by default, simply turning off the rules solved the issue.
In the Network tab in Firefox developer tools, there was a 500 server not found error.
Request: domain.com/?et_fb=1&et_bfb=1&PageSpeed=off
Response: (500 server error)
After rules were disabled, response code changed to 200 & Divi editor started working.