consider shepherds hook timing
Consider checking to see if the shepherd's hook (ramp that deactivates striker safety plunger by pushing it up) is timed correctly. If it doesn't push up on the striker plunger fully by the time you pull the trigger to the rear, you will end up with a light strike because your striker has expended some energy in wedging it's way past a partial obstruction.
How do you know if you are having light strikes? One way to check is to put a bic pen down the bore after you check that the firearm is empty and no magazine is installed. After you safety check a second time, point the gun upwards (it's empty, right? and nothing in the mag?) and with a charged striker pull the trigger. The striker will hit the back of the bic pen and send it flying upwards several feet. I'd say about 3 feet but I'm sure it's probably different for every pistol, just gives you a relative idea. Compare that with other pistols that you have. If you do this test repeatedly, the plug on the rear of the pen gets beat up and won't make good contact with the striker, so the decreasing movement of the pen will look like your firing pin spring is weak, so you may need another pen. I've used a chopstick too. But I've also had a negligent discharge doing this before so BE CAREFUL and always make time to safety check. Come to think of it, I think I was working on the very same problem.
If you need to open up the shepherd's hook, I used a screwdriver and wedged it in there, torquing it one way or another to raise up the ramp.
You could also remove and look at the striker to see if it's getting deformed from barely squeezing past the striker safety plunger.
I only know about this problem because I installed an Apex flat faced polymer trigger kit with FSS into my M&P40c, and had to adjust things by increasing the gap / raising the ramp of the shepherd's hook. If I recall, the Forward Set Sear kit came with it's own striker block plunger, which was taller and had rounded edges, instead of the factory angled bevel.
Then I purchased a M&P9c slide but the same FSS trigger kit didn't work with the new 9mm slide. The "new" M&P9c slide was actually older than the 40c I had, I believe, and I think there were rolling changes that affected the depth of the striker safety plunger as it sits in the slide.
Be aware that there is also an Apex Ultimate Striker Block sold separately that is different than the one in the Forward Set Sear kit, I believe the Forward Set Sear kit is the tallest.
The Shepherd's hook might not be your problem, but it might. If you want you could mark up the striker with marking fluid or permanent marker and see if there are surfaces that are rubbing when they are not supposed to. Permanent marker is a little fragile and might rub off by accident just when reinstalling, but it might be helpful. Good luck.
