NN3D with SC30, compass display roating

I have a NN3D 12MFD and a pc with MaxSea connected to a SC30 Satellite compass.
When starting up the system after shutdown, lying in a dock ship not moving, the compass display is rotating back and forth like mad :jump ? If the ship moves, like when "sailing"/ drifting slowly at anchor it show normal heading info. At the dock, compass display spinning, as soon as the ship moves the compass display start showing accurate info.
Check out this short video showing the compass display spinning:
https://youtu.be/y3Do00kZNV0
Any suggestions what to do to make the compass show accurate heading info at startup when the ship is not moving?

That looks like course over ground rather than heading

I agree, it looks like you have the ship icon set to COG (which is not valid information unless moving 3knots of better). Please check MENU - SHIP&Track Icon - General tab - Ship icon should be setup for HEADING. With a suitable heading input the boat should be correct when sitting still.

But of course. That was a real blunder from my side
Thank you so much for your respons.