I'm unfamiliar with the term "hammer drill" as applied to ARs. But from the other replies, it does sound like you're trying to fire faster than the rifle cycles.
I think it would be a bad idea to just blindly change out the FCG (or parts of the FCG) without knowing what exactly is causing your light strikes, especially when they're not very consistent or very common. Trying another lower is a good start; if you see the same sort of symptoms with another lower, it ain't a lower problem - unless the upper needs a different buffer. The first thing to try, whether it gives you the light strikes with another lower or not is to see how the upper reacts with different buffers. A heavier buffer will slow the cyclic rate, while a lighter buffer will speed it up. If the problem is that you're pulling the trigger too soon, before the bolt is fully closed, then a lighter buffer might reduce or eliminate that.
If changing buffers doesn't eliminate or substantially reduce the incidence of light strikes in these drills, then I'd suggest going with a completely new FCG, like an ALG ACT. I recommend this one in particular because there is almost no "break in" for the ACT, so you can discount any FCG function drag. For $65, it's an inexpensive upgrade over a stock trigger, and if you see fewer light strikes because of it, it should be worthwhile.