Reinstallation did resolve the issue because mvm.dll then was again 3MB instead of 0KB. My suspicion is that this error might occur again, and that it is related to the snakeoil that I am using to keep my system safe (Windows defender and McAfee).
THIS IS NOT A SOLUTION to the problem, but at least MATLAB 2017b can be made to work again. I hope this stays this way this time.
Best, Rainer