SOLVED!!!!
Turns our UCCNC were set up for running to fast. all axis moved correctly, but to fast and the A axis (and for some reason only the Axis) stumpled at these speed.
I found out as a noticed the joggin mode where set to 10% speed. When pushed to 100% everthing locked up.
I first tuned down the velocity in the "axis setup". Now I got moving and then noticed the movement didn't fit with the expected dictance. I then calibrated the axis and found the number wrong - changed it and where then able to tune up the velocity again.
Maybe I should have noticed this before - but I'm new and really happy to solve this problem