Gfx.WaitForPresent takes almost twice as long when a UWP project is built for Xbox (Screenshots attached)
Launching UWP build on PC doesn't seem to have this issue

To reproduce In Unity
0. Open user attached project
1. Execute Mainmenu > BugReport > Disable GPU Instancing
2. Open Player Settings and turn off Static and Dynamic Batching
3. Press File/Build Setting
4. Select "Universal Windows Platform" tab
5. Turn on "Development Build" (to be able to attach the Unity Profiler)
6. Build UWP Player with setting Target=Any Device, Build Type=D3D
7. Open generated .sln file in Visual Studio 2017

Visual Studio
8. Switch "Solution Configuration" to "Release"
9. Switch "Solution Platforms" to "x64"
10. Switch "Local Machine" to "Remote Machine"
11. Open the "Wolf (Univeral Windows)" Project Properties
12. Select the "Debugging" tab in the "Wolf Property Pages" dialog
13. Set the "Machine Name" to your Xbox One name or IP address and press OK button
14. Open file "Package.appxmanifest"
15. Switch to "Capabilities" tab in "Package.appxmanifest"
16. Enable the following Capabilities (not sure which of these is actually responsible to make the Profiler work): Internet (Client & Server), Internet (Client), Point of Service, Private Networks (Client & Server), Remove System
17. Press in Mainmenu > Build > Build Solution
18. Run on Xbox One

Unity
19. Open Window > Profiler
20. Connect to running Player on Xbox One
21. Note the "CPU" and "Gfx.WaitForPresent" cost
22. Close Profiler
23. Execute Mainmenu > BugReport > Enable GPU Instancing
24. Repeat reproduce list from step 2

Reproduced on: 2017.3.0a7, 2017.2.0b10

Was fixed with XDK updates.