And the good news is 17046 worked without a hitch...

Since I posted this I got it to work. I just clicked on the frozen window under the line above and typed 'e' (for exit) and as I did so, it continued and worked as usual. Either it was somehow...

UUP to ISO didn't work for me in Build 17040. It always gets stuck at DIR->ESD: Microsoft-Windows-Client-Features-Package with no activity in Task Manager.