Good morning Basj,
I have found the "problem": I wanted to try the START button on the left and other buttons somewhere else on the taskbar wich I did with the "configure START11 configure TASKBAR BUTTONS" where I selected "left START and TASKBAR buttons centre alligned". Now I returned to "centre alligned" and now it's ok again!
What I found is that START11 has different configuration menus which is confusing.
It seems that the taskbar is not as flexible anymore as in Windows 10.
Now that the issue has been resolved I thank you for your help!
Have a nice day.
Regards/ Jan