The tear drop shape on a primer fired in an M&P is normal.
Light strikes is something else. Are the rounds going off? If there are a lot of rounds through the gun when was the last time you removed the striker and inspected/cleaned the striker and its channel?
While you're cleaning the striker tunnel, turn the slide over and look at the bottom of the slide just to the rear of the breech face in the center of the slide. You'll note a small hole. This is a debris drain so any particles that enter the striker tunnel have a place to go. You need to clean this out as part of cleaning the striker tunnel.