I have all game mode functions enabled, and I am using UUP to update on my main desktop, and it is using right now.
So it is not the game mode functions causing the problem.
Correction, it has updated - one try only and it worked.
I'm wondering if 15025 isn't the first of the *major* differential upgrades, with the bulk of the download being a building on the base of 15019. In Linux this is the equivalent of a semi-rolling release...
Just on that point, it would be interesting to know how many have had difficulty going from 15019 -> 15025 as opposed to those installing 15025 from another starting point.
Here there was several hours of "Initializing" and thereafter I had complete confidence the build would install successfully.
However, after the update installs, the default is enabled again - much like the default browser being test to Edge is you user another browser as default after every update.
So, what he had done is faced the .Reg file that disables UUP and forces ESD on his desktop for easy access, so that after every build update he can easily disable UUP again.