I stay up to day on the APX and read just about every forum post as well as watch every YT video. I'm on the Beretta forum too. With that said, shooting low to the left is a common theme. I doubt it's you. I had the same issue. My groups were good, but just low left.
I made my post a year ago. But, I see your recent post.
I had to go to a large backstrap to stop low/left for me on the APX, after I changed the sights.
Gun was dead on with the largest backstrap. And, I have small hands, so that would not have been my preference.
Now, I've "discovered" the Gen 5 Glocks. I have not been a Glock fan for a LONG time. But, I sold that APX, and I got a Gen 5 Glock 19. I like the grip of the Gen 5 much more.