Having the same issue. We're starting up the first vault inside the Necralisk, completing it just fine with no issues. But then when we que up the second or third vault out into the world, once we get to the actual vault, it's repeatedly showing both members a black screen like we've fallen through the map and it's not counting as complete when we loot the vault. It does however complete it if we go back to vault one.
So completing every vault has been like this:
Complete first vault, no issues.
Do second vault, issue happens repeated black screens and character being