Both Rivensbane and Cursebreaker are extremely flawed with the time-gated RNG collection items requirements. I have now opened 41 (out of a potential 52) chests and still don't have 1K Voices and this is the only thing left for me to get Rivensbane. I appreciate having that "Gjally feeling" back in the game for great weapons but it's so demoralizing only having 3 attempts per week to try this just to get the title and extremely frustrating that I am unable to put in the time to grind for the requirements of the title. I really hope Bungie learns from this for future titles so that they can actually show off skill. I don't even think having RNG items as a requirement is a bad idea as long as you can grind out as much as you want. Ideally, we would have more options for obtaining additional keys. Maybe get an extra one every time you do a triumph challenge (I would sit and farm New Meta or hell even Petra's Run for additional keys).
I'm stuck in the same boat it's kind of annoying working to complete all the challenges and then be locked out of the titles by something out of your control