I finally got it last saturday. Was the first time I got two vaults but it does not pop the moment you “create” the second vault but when you run out of turns and the loot gets collected.
I got 1 Gem Key and 1.000 Gold if I remember correctly. So nothing out of the ordinary.
But just a few hours later I already got the first messages from other players, wondering how I got that trophy because it didn’t pop for them.
ceno