Pretty much like the Title says. I was in the Vault of Glass raiding on Hardmode and I used a heavy ammo synthesis during the death screen (while we were waiting to respawn after a wipe). I never received the ammo. I did however get the cool down timer. Same thing happened when I used a special ammo synthesis. It also happened to a guy raiding with me, who didn't hear me warn the group about it. It occurred at the Gatekeeper and Atheon checkpoints for sure. I'm uncertain, but it may have also occurred at other checkpoints.