Random Split screen zoom?

Is anyone able to explain what this is and how it happens and how to stop it happening?  Brand new S25+ only did smart switch from my old S21 yesterday.

The screen splits down the middle and magnifies itself, zoom in zoom out don't work, i can't touch untouch to fix it. The only way is to lock the screen and unlock teh phone again to force the screen to redraw.   It happens randomly while being used, and sometime randomly on its own just sitting on the desk. I don't have any way to specifically trigger it. It's not accessibility zoom as that has a blue border and you can exit that and i have that disabled anyway.