I'll throw my experience out there. You could have a tired hammer spring.
I always used CCI primers for my 70's vintage Python. CCI primers are noted as having hard cups. Utterly, reliable till one day. Explored the usual causes. No dice. As a last result, I had a new hammer spring installed. Presto, no more issues with light primer strikes. Biggest issue was obtaining a new spring. Colt wouldn't sell you one. Found a Master Gunsmith, in Redford, Michigan (Frank Paris) who was noted for his work on Pythons and HP's. He happened to have one laying around.
Prior to that, I use to go to a outdoor range in Mt. Clemens, Michigan. Passed by Magnaport, on the way. Stopped in and non other than Larry Kelly was manning the counter. He examined the gun and promptly said the problem was I installed an aftermarket springs and that was causing my issues............because the DA trigger was so sweet. Well, I was the original owner and gun had the same unaltered springs in it. Promptly, left and never went back. Wasn't impressed with Mr. Kelly, the owner and celebrated handgun hunter.