Got a Phantom 4 and have difficulties with a tiltet horizon of 2°-4°.
Calibrating the gimbal does help sometimes, but it can tilt in flight again and if corrected manualy during flight.
The amount of tilting can change so juo have to adjust manualy from time to time.

Someone got an idea?

This is a common problem many of us are having. Do a search and you will find a thread talking about this.

Someone suggested the tilted horizon is easily corrected by holding the C2 button and scrolling the wheel on same side back and forth until horizon is level.

Sorry for the inconvenience caused, romankasperski. It is a known issue and we are working for the solution.