If you encounter these problems during a phone call:
Screen immediately locks after answering the phone.
Screen still locks after the call ends.
Check if your screen protector, if you're using one, is the culprit that's blocking your proximity sensor. Please note a screen protector with no hole on proximity sensor position may lead to a malfunction of proximity sensor. Remove your screen protector and re-confirm if the problem still exists.
The proximity sensor is usually located beside the receiver. We recommend you to use a genuine screen protector sold by ASUS.