I would recommend updating your phone's firmware to the most recent if you haven't already.
At the time of this post, that is 1910.44 for worldwide. If you are not on worldwide, please check with your regional support site.
ROG Phone II Driver & Tools | Phones | ASUS USAIf a FW update doesn't resolve this issue, you will need to contact your local ASUS repair center. The fact that you have had this issue since you started using the phone points to a hardware problem.