Ammo available, but no bullets in magazine

I just played my first campaign match and accidentally picked up a 9mm gun from a dead Merx. I thought I could equip 2 pistols at the same time, but doesn’t seem to be the case.

Anyways, fast forward to the end of the match, I emptied my magazine and the game showed that I had 130 bullets left, but nothing happened when I reloaded my gun. I held R and it showed the animation of taking out the magazine and it was empty, and at one point my gun “reloaded” but every time I tried shooting with it, it would make the click sound as if it was empty, but I saw the number of bullets decrease on the HUD.

At one point I stopped shooting and the bullet number was decreasing, and it looked like it was counting the bullets from my teammates.