Make sure that the FPB can move freely. Maybe it has been peened by the firing pin. Possibly a too tightly set trigger stop could do that. However, in my case old dried low quality oil and cold weather was enough for rack-bang.
Or just leave the FPB out. Put mine back in my old Witness only because of IDPA rules.
In addition, if the fpb does not move freely it will trip the sear when the slide goes forward. Gun goes bang when you rack the slide. Nasty on the range, potentially deadly in an empty chamber carry/home defense scenario.
I guess this case is settled. But if you have issues with your Tanfo going bang when it should not, note that a sticky firing pin block may also trip the sear when the slide goes forward. Unique to the Tanfo FPB system where the FPB spring actually helps to trip the sear.
Rather just lower the hammer completely and let the inertia firing pin do its job as intended. If dropped on the hammer the half cock notch might shear of and the gun go bang.
There was a reason why the Colt SAA was carried with only 5 rds instead of using the safety notch...
Have you thought about machining it to take plates for the optic ready model? That would give you narrower screw spacing on the slide. Obviously the plate would overhang on the sides, but that should not be a problem.
DLC was originally developed as an industrial anti-friction / anti wear coating. Cerakote was developed... I don't know. To offer finishing with a modest investment and have nice colours?
The only explanation for this accident I can think of is that the firing pin was longer than it's channel. Are extended firing pins really this long? This would completely defeat the inertia firing pin principle.
The sp-01 / Shadow 1 rod is too short, does not reach into the hole of slide front. Dry cycles ok but did not want to try shooting it.
Maybe a CZ97 rod would fit? Or any competent gunsmith or machinist should be able to make one on a lathe.