I finally found time to do your very helpful scientific experiment.
Was to complicated for me. 
But for anyone else having this problem:
My z axis minimum was set to z0
Changing M208 for Z0 to Z-2 in config.g was finally solving the problem.
@atall thank you all for your great and quick help, tips and tricks.
After 10 months of guessing and time consumable troubleshooting I am finally able to use my most expensive printer!
hooray!