Solved Trouble with the builder on one specific machine

My client is having an issue with Divi Builder and we can't seem to track it down. We were getting the "Your Save Has Failed" error on both our machines (we live in different areas) when trying to update a page. Google to the rescue: clearing ChromeDevTools>Applications>[Site]>Local Storage made my machine/network functional, but my client still can't perform edits after donig the same.

Sometimes they get the "save failed" dialog. Sometimes they can't double click anything to open Divi Builder. And all the time, if they ever try to save/commit a change, a new tab is opened with an ERR_CONNECTION_CLOSED. This closed connection never happened at all on my machine (so I assume it's a different issue altogether), and none of WP, PHP, or Apache's logs are showing any obvious reason for it. There're no blocked IPs. We've tried deactivating relevant plugins (including security), updating the Divi theme, updating WP, using Edge instead of Chrome, (they were able to double click sections to edit, but still ended up with the ERR_Connection_Closed tab) and disabling their firewall. We're running PHP 7.4.

Any thoughts would be appreciated. The site is accessible so there's no downtime involved, just an inability to update content reliably.

We're using the free version of Divi.

 

As it happens, you have solved our problem! Thank you! The issue started happening on my machine shortly after I posted, so we started using Divi Safe Mode (which was a successful workaround, but just that). I have now backed up and cleared 2500 revisions, and limited revision counts sitewide. Both me and my client are able to edit via Divi. Hopefully this will be all that's needed!