u/Various-Airport-8421

I have a Mark 4 22/45 less than 6 months old that I've zeroed 3 times. I put witness marks on the elevation screw and sight last time I shot (75 rounds) and it lowered 2 clicks. The last time I zeroed it was lower by 4 inches. It's only elevation that is affected.

Has anyone experienced this? Ruger said it's not a known issue nor have they heard of this. I don't believe I'm influencing this with any storage, "bumping" the elevation screw etc...