In patrolling mode when if angle is in range -20..20 then
robot should move front and if angle is greater than 160 or less then -159 backward. This fact costed me 15 submissions. Hope it will help someone.

>>if angle is greater than 160 or less then -159 backward
You aren't right.  Angle must be >= 160 or < -159 (<= -160).
I fixed this and got AC.