The screen on my Alcatel Idol 3 goes black when making or answering a call. This suggests that the proximity sensor may be bad. The Phone Tester app indicates that the proximity sensor reports "near" all the time. A customer support rep had be do a reset (edit: wipe system cache) on my phone (not factory reset). This did not resolve the problem. He then suggested doing a factory reset and get back with him to submit a warranty claim if that didn't work. What are the chances that a factory reset will resolve this problem?