Warm phone when i use AR and position unfixed.

Hi everybody
I have a problem. When i use some app i see that AR is working good. When i use my app at AR from unity my phone is worm stronger and position AR models may move. Whats wrong?

The augmentation should not move from its exact detected position, even if I move or rotate the device camera away from the Image Target.

In unity, I have used the ARCore and able to detect the image target.

How to stabilization detected position?

My phone Galaxy S8.

Thanks.