If you're standing on the elevator that drops you off on a new floor it seems the bullets get blocked by invisible walls. As soon as you step off the elevator tile, you can shoot through it just fine. As soon as you step back on the tile, however, my bullets disappear and don't hit enemies. I'm using the Cryotech Alchemer MK II, and the bouncing shard that breaks off functions normally, but the primary bullet doesn't seem to even exist.
I don't know if this bug is related to the gun because the bouncing projectiles have some odd effect, or if it happens to all guns.
It's reasonably safe to assume all guns. I've had the same issue with my Protogun, Autogun, and Blaster in the past.