Hi, Geez! Thank you for looking into this issue. Thanks to Dimas008's comment:

In T143590#1935531, @Dimas008 wrote:

Have you guys tried to hold R button to perform unjam action?

In T143590#1935178, @Col_Kernel wrote:

This also occurs:

• with other guns (tried it with the MK II and the FX-45)
• if you go prone during the reload animation
  
  Not only is the gun bugged, but you can't interact with objects or open doors etc. either.

In T143590#1935044, @rlagudwns26 wrote:

Thank you for explain better than me ;)

I can confirm that this bug can be reproduced. When single-chambering (single loading) a bullet into Mlock, if I jump during the animation, the Mlock in my character's hand will be bugged. A bugged pistol cannot be removed from hand nor chambered again. Drop or throw will not work. Drag into inventory or ground won't work either. No magazine can be combined with it. It will not fire, even though one bullet seemed to be removed from inventory. And if there is a stack of ammo in inventory, its number will indicate as if one bullet was removed from the stack. The stack in the inventory couldn't be interacted with after the gun was bugged. Only logging out and joining back in the game can resolve the above issue.