Windows 10 None of my games use Fullscreen Optimizations

[BE477]

For anyone that doesn't know Windows 10 should automatically run fullscreen games in a borderless windowed mode for faster ALT+TABing which they call Fullscreen Optimizations, but for some reason I've noticed that Windows has stopped running any of my games in this mode. I've tried Googling a solution but the only posts I can find are from people that hate this feature and want to disable it, but I would like the convenience of being able to ALT+TAB without my games crashing. Anyone know what the problem might be? Thanks.