Since Redstone 3 (currently build 16170) will supersede Redstone 2 ("Creators Update" version 1703 build 15063), herewith a new topic.
As I reported here, no success yet with updating.
Update 17.4.2017: 16176.1000 successful after several attempts.
Solution may have been that I finally turned off 2nd monitor before updating; 2nd monitor OK after update.