Altitude Hold Problems

Hi all.

My octocopter ( X8 configuration, MN3512-KV700,12*5 Aeronaut; Maytech 30 A ESC; 3DR Pixhawk (SW 3.2), UBLox 8 GPS ) shows a really strange behavior in AltH + Loiter.

What is happening now is that Altitude Hold and Loiter are unable to maintain a consistent altitude. When I keep the Copter hovering in place (either by manually doing so or using loiter), I get an altitude change of +/-1-4 Meters ( look like a bouncing ball ).
This is a bit of an issue but even more so is that when I fly it laterally, it looses altitude very quickly until the pilot corrects the throttle manually.

The measured maximum vibrations are about ± 3. So it doesn´t seem to be a vibration issue.

Sorry, the original Log is too big to post.

Any ideas?

Thank you very much!

Best regards