Apparently there's some rollbacks going on.
There is a certain time window during which you can actually be "out of the game" and still comtinue vMA. I dont know how long it actually is, but I think it ranges somewhere between 5-10 minutes. If your logging back in took more than that youre kinda shrekt.
Regardless I think vMA resetting sucks no matter how long you are offline. There is no reason for players with less playtime to be essentially gated from this content when the tecnology is there to make it possible for them ( see normal arena).