Motion detection intermittent

Hi I have a system at my place that’s working well. I have just installed a system at my daughters place but the motion detection isn’t working properly on a couple cameras. I have set up up in as many variable combinations as I can think. It seems to be intermittent. One day I will get her walking out in the camera view but get no car movement after she enters her car (all motion) next day I get the car motion and no alert of her movement. In the mean time I am getting cars and people moving out on the street 40metres away. The cameras in question are pointed fairly well down from a height of about 10ft. The other two Cameron the system appear to be working ok. She does have bushes in the problem camera but I have tried activity zones to block these out. Have tried a reset but no help