There's a pretty common bug, I think it happens 100% of the time, which is that when you use smoke grenades, the fragmentation grenade slot gets replaced by the smoke grenades, making it impossible to use them unless you open your inventory, throw away the smoke grenades, and then manually put the fragmentation grenade back in the slot. This makes the whole process very time-consuming and tedious, even more so when you're in a confrontation where speed is essential.