I’ve just had a similar problem with divi not saving properly except that the page data was being saved to the database but when the page was viewed it was unchanged. I found the firewall was blocking me as a potential hotlinking threat. I added a firewall rule to allow my IP address which fixed that part of the issue but it didn’t fix the saving problem.
I’ve finally tracked the problem with saving to having a Page Rule set to “Cache Everything”. This is very unusual because my first page rule is to bypass caching for anything in the backend (/wp-admin*). I was expecting the divi pagebuilder to trigger that but it doesn’t seem to for some reason and the old versions of pages are somehow still served.
I also found a workaround which may interest you if you also have the cache everyting option set. In the divi Theme options go to the page builder options and turn off the “New divi builder experience”. You will then be editing with the old page builder but it seems to work fine. The alternative is to change the caching level when you want to edit a page with divi.
I spent a few days trying to get to the bottom of this with ET support and finally found it last night. Not sure if this will help but I hope you’ve solver your problem.