Arducopter loses Altitude in AUTO mode

Hi, there !

My Pixhawk Quadcopter looses altitude while in AUTO mode for some time and then gains it despite the same altitude set for all the waypoints.
Voltage seems to appear almost same through out.

What could the reason be ?

Can’t say much without on-board log.
Try increasing Z controller’s P gain.

Hi @Mustafa_Gokce
Thank you once again for the reply.

Here is the log file.

It’s the last AUTO mode mission in this log: where the altitude went down and then went back normal.

It’s premature to run an Auto Mission when:
You are on very old firmware (update to latest Stable). What Flight Controller if you are using Fmuv3?
You have not done the Initial Parameter Setup which is meant to be pre-maiden flight and located in the Mandatory Hardware section of Mission Planner.
So as expected tuning is poor, motor outputs are oscillating. Your Z-vibes are high also. You need to get the fundamentals straight before attempting an Auto Mission.