OutbackMan said:
I'm pretty good about checking arrows and nocks for any damage
As you said, w/0 pix or vid, it's tough to know exactly what's going on; but I have to believe that in these instances you missed some prior nock damage. Perhaps it was not as severe as the end damage, but enough that the consequence was total failure.
As you didn't say, I have to assume that you use one nock point, and that you nock your arrow below the nock point? I'll also assume that you use the metal "squeeze on" nock points so common in the industry?
My recommendations: get rid of the metal "squeeze on" nock points and use a'tie on' nock point. There's probably a "how to" in the, what else, :D "how to" section of the Forum.
I fit my nocks so that they have a sliding fit, but will not stay on the string when I let go of the arrow. I, too, shoot split finger. I set my middle finger firmly against the bottom of the nock, when setting my 'hook',so that it applies light pressure to the nock against the nock point. My index/top finger makes little to no contact with the top of the nock, so that I am not pinching the nock between my fingers. I have never had a "dry fire" using this method.
You might also check your drawing hand at full draw in a mirror, or have a friend check it for you to insure that the back of your hand is flat and that you are not torquing the string.
Good Luck, and Good Shooting!