i would suggest testing in different conditions first. it could be that the area you are testing in is not tracking well (i.e. low light, not enough for the camera to recognize and track such as glossy surfaces, etc.). Also, have you checked that the image you are using to track with is "good enough". I use the ARCore Unity plugin in a separate app to test the rating of the image; i don't use anything with a percentage less than 80 in my apps.