I too encountered the same issue today and here is how I solved it.
Step1: Looked at Divi->Support Center at my WordPress Dashboard for any error listings.
Divi Support Center
Which clearly told that wp-content directory was not writable. To confirm furthermore followed step2.
Step2: Enable WordPress Debug logs in wp-config.php as below:
define( 'WP_DEBUG', true);
Now I saw below errors in webserver log files:
2020/01/08 10:48:49 [error] 18271#18271: *2598 FastCGI sent in stderr: "PHP message: .../cache/Directory.php:65 ET_Core_Cache_Directory::_initialize():
Unable to write to the filesystem. Please ensure that PHP has to write access to one of the following directories:
- WP_CONTENT_DIR
- wp_upload_dir()
- ET_CORE_CACHE_DIR" while reading response header from the upstream, client:
It was more or less clear that because of not writable to WP_CONTENT_DIR by the webserver, the timeout occurred. Provided the required permission to the user which is running the webserver (in my case Nginx) as below:
#chown <username>:nginx wp-content/
#chmod 775 wp-content
Now it started working. Hope this helps. This is because Divi creates a directory called et-cache inside wp-content dir for performance enhancement by generating static css file which is cached in the et-cache folder.