Exactly the same thing is happening for me. I Stopped playing the game before izanagis came out and then went back once shadowkeep came out. I saw everyone was using this sniper and watched how to do the quest line. But when I went back to ada after opening the 3rd lock she wouldn't give me the key mold. This is a really annoying bug that becomes more infuriating when you realize that the step after that is trying to get an rng bounty to drop from ada. So instead of being able to grind those out we just have to wait until bungie fix it and then we have to also grind for that bounty. Hopefully it doesn't take till the end of the season for them to fix this.