I have a large list of installed mods in Payday 2 and recently I have noticed that some weapons don`t pick up ammo, according to More Weapons Stats. As I click on different weapons, the ammo pickup rate decreases until it reaches 0. These weapons are vanilla assault rifles with DMR kits and some custom weapons. 
I wanted to know if somebody had the same problem and/or could help me to solve this.
Thank you beforehand.