Volume down and Power key not working occassionally

I am currently on 6.0.1 build MOB30G stock. At times the power and volume button don't respond. no matter how hard you press them. If the screen is locked, the only way to turn on the screen is to get a call or attach the charger or simply press the power key for 10 seconds+ and the phone restarts. Rest of the time the buttons seem to work properly. Judging its more of a software problem than a hardware one , I have done a factory reset on the phone.. but the problem has reoccurred. I believe a recent ota update may have caused it.

Any one else facing the same issue?

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