Visual builder not working on home page only, Divi 4.17. 4

Hi guys,
I am unable to enable the visual builder on my home page since the latest update. When I press the enable visual builder button it just loads the page again without the builder. If I go to edit page , I cannot open it in the front end view. It just loads the page like normal.
I have cleared the cache, tried in safe mode. Disabled Static CSS File Generation in theme options.
Spent an hour with my web host looking for errors.
The only clue is if I look through the inspector when the page is loading, it has a 500 server error. But our webhost does not see any error at his end. Like it is not even reaching him.

Things I have found out through troubleshooting:

If I roll back the Divi version it works, then if I update it again it stops.
If I have a non home page the visual builder works, but if I make that page the home page, it will not work, make it non home page, it works again.
I made a basic no frills page the home page just encase a module was the culprit, but as soon as it is the home page it stops working.
This is happening in our main website and our dev site.

It seems to be our site url and '?et_fb=1&PageSpeed=off' on the end is not working in Divi 4.17.4. It wont enable visual builder. Doesn't matter what page is the home page.

I am hoping someone has come across this in their travels as I don't want to be stuck using Divi 4.10.
Thanks
James