TLDR: change the aspect ration of your camera component in the ARpawn
I have been struggling with this as well, with the help of a few comments here I was able to narrow it down to an issue with the aspect ratio on the camera in the ARpawn. If you aren’t comfortable using the language of the old gods and changing the foundations of the known universe a far simpler temporary solution is to simply change the aspect ratio of the camera in the ARpawn. Jeffrey mentioned you can do this in blueprints, which is true, and you can change it in the Details panel under Camera Settings. (Or just search for “aspect ration”) Also the Value is a float so just divide the ratio. I tested this in portrait mode and landscape using the values 2.16 (for landscape) and .46 (for portrait) on an Iphone 15 pro max. And it worked much smoother and was more accurate. I was not using the default AR, I was using marker tracking and facing a similar issue. Thanks everyone for the help!