The Quest disappeared completely from my inventory and I have checked everywhere for it. Postmaster, drifter its gone, tried on another character and same thing. It's been a known issue but Bungie hasn't done anything about it.
Hi. Thanks for your report. This issue occurs when you pick up the quest on a platform that owns Forsaken then you try to complete the quest on a platform that doesn't own Forsaken. You can reacquire this quest by defeating an Ascendant Primeval on the platform that owns Forsaken. You will have to complete it on that platform, too.