Dip in altitude without inputs

ArduCopter Copter 4.0
1

I have checked the following in logs:
1)GPS and ekf seem working fine
2)rangefinder has status shift to 2 midflight
3)Copter has dipped without any RC inputs, which is happening because DVD is positive. Why is DVD positive without any inputs?

I am talking about the dip between 13:56 to 13:57

logs

2

You posted in the 4.0.x forum section. Are you using ArduCopter 4.0.x?

You should be using ArduCopter 4.3.6 and posting on the ArduCopter 4.3 section of the form.