The Stat Tracking on C4 shouldn't exist as it's a one time usage item and it explodes because it is currently breaking stack sizes from StackModifier Paid version plugin. If you try to stack it with other C4 stacks even though it's nowhere near the limit it will not stack because of the different IDS given to this item. It also appears to happen to medical syringes somehow as well as have noticed. 

could you maybe add config options to make an allow or disallow list in the config so we can remove items we don't want to stack like C4? Or maybe just fix the stacking issue somehow.