This problem has been brought up on the Discord, but I'm posting it here for good measure.
In the current UWP version, a virtual mouse must be used once per unsuspended state. Winjs has since been updated to change the way a pointer down state works. If you switch to the latest version of winjs, you will need the virtual mouse to be present in each frame to achieve 60 FPS.
I'm uncertain if this is a Fusion issue or a WinJS issue.
This will happen on a blank frame.
Hope to see this get resolved!