Hey Julian,
Thanks for your compassion 
Did a quick test on my son's Windows 10 pc (please don't tell him 
), and there it was working fine. Finally I saw a difference between both pc's. On mine, the developer tools showed some mobile related stuff on top:
Seemed I had turned on the device toolbar:
And that introduced the touch events, which are not wanted in a debugging context (since Android Chrome has no developer tools). So that is why the touch-related error popped up...
After turning off the device toolbar, everything worked fine again.
Again an evening wasted ...
Case closed!
