Hi, I found a workaround that just now fixed it for me!
essentially I rolled back the update of 14915 to 14905 as follows:
Hit Windows-i and choose “Update & Security”, from there you go to “Recovery” and start the process of “Go back to an earlier build”.
During that process it will ask you to provide a reason (checkbox is enough) and it will ask you if you want to searc hfor updates INSTEAD, for that question you choose “no” and continue with the rollback.
Be careful to save all your open files, close all other programs as it will immediately reboot your computer after the final notice! 
The rollback itself took less than 5 minutes for me and all the menus in UE4 are working again.
As a side note: in Win10 redstone 2 insider preview build 14905.1000 the windows context menus are broken.
You can use Windows key + X to get access to the sleep and reboot functions and check back later.
I also contacted Microsoft Support about this issue and they assured me the broken incompatibilities with UE4 (among unnamed others) is known to them and a fix is already in the making.
Have fun and stay unreal!