Ever taken the bolt apart and cleaned it internally?
^^ Yes. The first thing I'd do is this. Take the bolt apart, and clean it inside. Make sure there isn't any debris inside. Have you pierced any primers or blown any primers since you have had it? (some light primer strikes I have had were after some pierced primers or blown primers, from the gases blowing crap back into the bolt and trigger area) I've had the small part of the blown primer clog up my firing pin, and have light primer hits with no round going off.
Also, clean the trigger with some brake cleaner or lighter fluid. Use a heavy flush of it. When at the house, it's hard to diagnose it, since you can not fire it. I have loaded up some empty cases with only a primer (no powder or bullet) to check for the "bang".
If it's not making good contact with the primer, it's usually inside the bolt, or from the trigger. And check the trigger to make sure you are not missing any set screws. I have lost 1 important screw on the trigger, and had an issue once.