I was drinking a soda from my inventory then i went on to the next soda in the inventory and drank it but nothing happened so i canceled the animation.
I started walking and the animation for putting the gun on my back started playing and after that my gun was stuck on a weird position in my hand and vanished when i switched to the shotgun.
You can see it all in this video https://www.youtube.com/watch?v=PV53KmytyIA&feature=youtu.be