Weapon disappeared in middle of battle

Just ran into an interesting problem here…
I was in the middle of the captain haunt fight again, when the electric smg I was using vanished from my inventory. I switched to a rifle, then when he got his shield back I went to sweetie back and it wasn’t there. I opened my menu to find that slot had nothing in it, and the weapon I had been using was not in my inventory.

And another randomly vanished item… Lost an artifact between putting it in the bank and it getting there… Think I best log for the night…

We’re you using Moxxi’s Crit SMG with the red text: ‘slippery when wet’?
If so, you have an increased chance to drop that gun on reload.

I was… I didn’t realize they was a chance to drop weapons on reload… Guess that answers that question, thanx!