The problem with 2FA is the security.
example : 2 same email addresses in the database is forbidden.
All Frontpage designs must be compare to the new security rules.
(i deleted all html data and proceed with a blank page)
I saved all content pages again.
set mode to production.
When after above checkups you do the normall cleanup (c:c c:f setup:di:compile ect)
For me all was good,
Now i noticed there were more problems with my HTML.
example in the banners above the catalog they were not well programed.
For me i think it was all little issues together that make the page load fail.