So I had 2 guns. 1 Spec Ops Silenced SCARAB and 1 long-sight SCARAB. I recently replaced the long-sight for a Silenced Marshall shotgun.

Now, my spec ops scarab is out of ammo and I can't refill the ammunition using the ammo stockpile. I also can't switch my shotgun for another gun (was trying to switch it for another spec ops scarab).

What the hell is happening here?

You mean loadout pro?

Well, for the first - you can't have 2 scarabs in one class.
You might had SCAR and SCARab in one class? That's might be.

about not reloading issue - can't tell anything.

I too can no longer refill my Scarab after the part where we are captured.

I've switched to a new Scarab and same thing. 40 / 0 ammo and won't refill.

This is happening to me also - totally game ruining experience!! I can't use my favorite gun now.