Thanks for the detailed response. I can confirm that I have "unredirect fullscreen windows" set, "detect refresh rate" disabled and refresh rate set to 120. Technically this isn't twice my TV's refresh rate. If I type:
nvidia-settings -q RefreshRate
Then I get:
Attribute 'RefreshRate' (rossmoore-server:0.0; display device: DFP-1): 59.80
'RefreshRate' is an integer attribute.
'RefreshRate' is a read-only attribute.
'RefreshRate' is display device specific.
'RefreshRate' can use the following target types: X Screen, GPU.
But I can't set the refresh rate in compiz to a fractional number. Is this the source of the problem? Or is it related to the fps of the material I'm playing?