On the campaign in the boss room where you right the harbinger the kinetic ammo wouldn’t work. It said my gun was already full when it had 1 clip left in it. I tried dropping the gun and picking it back up but still was doing it. The picture of the bullet above it had also disappeared but was still lighting up orange.
I had something similar happen to me. I was on the mission “The Sequence” and went to kill the HVT Zeretus. I had a shock rifle with low ammo but the shock ammo crate said I had full ammo.