Proximity sensor not turning off screen

[xtsubarublazin]

Recently I've noticed my screen not turning off during a call so it's easy to accidentally end a call. Must be the proximity sensor. I have restarted the phone and it eventually happens again. Any ideas? I don't notice any dust in the sensor lens.

 

[Muessig]

Do you have a screen protector over the proximity sensor? My brother had a similar problem to this on his 820 and the screen protector turned out to be blocking the sensor.