Unreal Engine 4 is available for Win10 UWP app dev now

The logfile mentioned should be in Engine\Programs\AutomationTool\Saved\Logs. What does it say? In particular is there an error code from signtool? Common cases are here.

Also, not sure what commit you’re on, but a fairly recent one added a button in the project settings UI that will generate a certificate for you. You might see if using that makes any difference.