I have just two TK clips (they were furnished with the gun) and on the first day my cousin and I both had a few misfires. If trying Federal ammunition doesn't work I'll contact S&W.A 986 in stock form shouldn't have any issues with light primer strikes. If you have removed, cleaned, and inspected the firing pin and firing pin recess as previously suggested, I'd contact S&W and request a return label. Factory DA trigger pull weight on an unmodified 986 is probably in the 11-12 lb range. Winchester primers should still have reliable ignition even when lowered down into the 8 - 8.5 lb range. Absolutely unacceptable to be experiencing the issues that you are having if you haven't installed a reduced power spring kit.
Did you have as many light primer strikes with the stiffer TK clips?