I had the issue, that i shot with the amphibia S, but the bullet didnt disappear. Shooting was not working with that already used bullet, but when i unloaded the bullet it disappeared and on the left was the message that the gun is already empty. Same issue with the next bullets.
I should have tested it more, instead of throwing it away..

Edit: spelling

are you able to punch when you have this issue? (ie, holster your weapon and use fists)

I think it's a common bug, i've heard about it and had it happen to me a few times, only way I was able to solve it was to completely exit out of the game and reload.

I had this issue with a double barrel shotgun... but no amount of reloading, dropping ammo, dropping gun, splitting ammo, etc would fix it... then I handed it to a friend and he was able to instantly fire it.

I had a problem with my mosin that it wouldn't fire, so i unloaded the bullets and put them in again and it worked.

I had this issue with almost all the handguns at some point. It happened to me when I chambered a round and fired. Then the round was just stuck and I could not even drop it out of my inventory. I had this issue with the 1911 and the FNX so far.

I had this issue with P1 pistol. Couldn't fire or aim down the sights. Tried with full magazine and single chambered round. Other weapons worked normally.