the last problem was, that the developer tool was crashed and did not reload the changes.
no error message etc.
Restarted and it was working immediatelly.
So I will keep this in mind and reboot the Developer tool more often 
i know this is late but is not this restart the tip to soft round or something. i think i try this but change from my costume shape to round for some reason. it work so can get the uxp change some brush setting but not well for me i dont know