It was not the same board, just a similar one... The settings are different, because it is a different machine. Slow speeds with the other cnc and kcam was possible without any problems.
I just tried to set the microstep back to ½ step. Apparently it works better... not loosing so many steps. But I just tried it quick, i will do an attempt some day next week to see if it really helps.
But is it normal that steppers runs smoother at high speeds?