This looks like “bad” RNG to me, not a bug. A vault has a chance to award you Gem Keys, but it also has a chance to award you one of the other “prizes” on that particular line (Glory, Glory Keys, Gems). You’re not getting the drops you want, but that doesn’t mean it’s a bug. Just “unlucky”.
Those chests in Treasure Hunt are basically just another set of loot boxes, you randomly get one of the listed rewards. Infinity Plus Two keeps the drop rates secret, which usually means the Good Stuff has such ridiculously low drop rates that listing them honestly would be considered bad publicity.
Watch carefully as it’s cashing out the board and you can actually spot what each tile drops – in this case, the “6 Glory Keys” was one of your drops from a money vault tile. (Note you had no red chests at the time, and they drop Glory Keys in twos.)