Call can't be pickup!

Sometimes i cant pick up the call...whenever i try to answer the call its cant be pickup and show as missed call??
I m on CM13 Android version 6.0.1 ...
Whats the problem in my phone??
Before flashing CM13 I was on same problem in lolipop 5.0.2 stock version ..
So plzz guide me to troubleshoot this problem??