There is the excact same issue posted on the US forums. But support told me report here.
So basically i just went in on my alt yesterday and did a quick ++2 key, the 0/1 mythic dungeon was still greyed out afterwards we finished the dungeon. So i tried to relog, restart etc but nothing helped, i just had my fingers crossed that there would be a reward for me in the vault this morning, but still nothing. Please do something about this fast, because if this continue im done with the game.
No point in doing keys if there is no weekly reward anyways.
Also, a weird thing is that raider io does acknowledge my key but the vault does not 