I was playing Decapitation on ruthless and had found and picked up the Gene seed behind the elevator right before the section where you drop the bridge on the Hive Tyrant. Upon crossing the bridge and exploring, I had found a guardian relic on the far end of the arena (the side closer to the roof tops where the tyranids drop down). I wanted to leave the gene seed on the ground in case I was incapacitated so we could grab it later. upon switching the Gene seed with the guardian relic, the gene seed immediately clipped through the ground being lost forever.