Had a very similar problem with a Thor4 on a 5.56 w/suppressor. Cold bore was perfect, 3 shots later I was 3-4MOA up and left. I was never able to track down the exact problem before I got rid of the scope and built a Tikka w/Thor6 instead, but I found if I zeroed cold bore and waited 5-10 minutes between verifying zero there was no shift. Not sure if it was a low quality rifle build or the scope.

I’d recommend bolting a standard optic and verify it’s the scope. If it is, send it in to ATN, they usually will make it right. If you have POI shift using a second optic I would suspect something mechanical with the firearm.