Hi, I'd just like to report that I've experienced this problem intermittently as well and after researching it, there may be a problem with the touch screen's calibration. I haven't been able to figure out when or how the screen is calibrated, but from experience, it seems to re-calibrate itself upon waking up from sleep. By having a finger or hand pressing on the screen accidentally when waking up the phone, the calibration could be so far off that your finger is not recognized on the screen. As a first step, try to leave your phone screen pointed away from your leg in your pocket and avoid touching the screen when someone calls.
You can also use a bluetooth headset's call button to answer your calls, but this would obviously drain your battery on the headset and phone.
Haven't been able to find an ACTUAL fix though, besides double-clicking the lock button and rejecting the call, then calling them back while they're talking to your voicemail... 😟
<Edited by Host>