I also have a SuperNova Max 4 camop and have never had this problem. I am selling mine if anyone is interested as well.
I agree, you must be pulling on the forearm. Have you shimmed the gun at all? You could add the shims to the gun so it pulls more from your trigger hand.
I have shot 2 3/4,3, 3 1/2″ shells with no problems. Gun is great, but this one just doesn’t fit me well and I keep missing on moving targets. This gun just might not fit you very well. Might be too bulky for you to use.