I acquired the Drain, Irrigation, and Conduit keys while playing the Leviathan raid in Destiny 2 today. At some point after receiving the third key (Conduit), I noticed that I no longer had the Drain or Irrigation keys in my inventory. The item drops popped up on my screen when I received them, my inventory was not full (9/50), they did not go to the postmaster or vault, and I did not dismantle them. Another member of my raid group also experienced the same issue during our raid; the remaining 4 did not, and have all 3 of their keys.