I got same issue . only difference now is that it`s present to all my character 
So Murozond’s Rise working now but today I receive key Galakrond’s Fall fall and again cant que becouse it’s still bugged. It’s almost month and still no repair. So now I’m paying for game that I can’t play properly to next reset.
Fix on mythic + Locked Keys is to change it`s dungeon type frome NPC at the end of Dungeon.
PS: Key needs to be same lvl or lower then M+ dungeon.
Same issue here.
Galakronds Fall - “One or more dungeons was not valid” when trying to list the key.
Are you serious? I get this key from the start of the patch every week, it’s some kind of mockery! I tried not to open the vault, went to the m+ dungeon and in the end the same key fell out again 
Still no fix 
Can’t make group, can’t get rating becouse of that and that makes things more dificult to find group to other dungeons.