may we ask even after a full game restart hasn't the item appeared? In case of item disappearances they should be put back automatically. You may find it in your inventory please check on it!

For me, the weapon never returned. An Exitus rifle disappeared in the last step of fusion 72-100%. I collected new Exitus and fused 100% successfully. Later it happened at some item, I don't remember which one. It's random.

Okay