I am sorry BUT … why so many issues? And why didn’t you there at Epic Games just mirror the whole forum database to another server and beta-tested the upgrade there? When it was ready and only you should have migrated the main live forum to the new fully tested version. At that point it would have been trivial regardless of any new data in the forum database because it would have been highly unlikely that any changes could have triggered any bugs not covered during the beta-testing phase using a days or even months older copy of the forum database.
I really don’t understand why you are doing all of this… I mean this way… why? You are developers of one of the most advanced 3D engines on the market and you can’t figure out how to do some proper beta-testing of your own forum without disrupting its functionality and users/customers use of it ?
I mean, along with the whole marketplace huge slowdown issues all of this doesn’t look good marketing wise, at all. You should absolutely avoid any of this… you are not a small or tiny indie software house and you aren’t a single guy a single freelancer with his own apps and personal forum to support customers or anything like that so people would accept the issues mostly understanding that a small business would need a lot of time to fix things up.