You need to cap FPS @ 57 for Gsync to remain active @ 60hz. Same applies to 120 (117FPS frame cap). The reason you're not noticing the tears at 120hz is because it's less frequent.I have a 2080 ti, and have been using Gsync via instant game response. The reason I was looking forward to potentially using Freesync is its low framerate compensation. I like to play at 4k max settings, which even on a 2080 ti can cause dips below 40fps in a number of games.
Beyond that, I'm also having some issues with Gsync which I was hopeful if Freesync was an option could possibly solve, but seems this isn't an option so I'll instead speak on my issues and hope others have any ideas.
My first issue is the in-game settings for games seem to make use of only the resolutions listed under "PC" in the NVCP. This is an issue because, for example, the 3840x2160 resolution under PC is limited to YUV420 8bit as it only lets you choose a refresh rate of 100hz or 120hz. The 3840x2160 in the list above PC tho lets you select 60hz and thus YUV422 at 10bit for HDR.
Additionally, if I do choose a lower refresh rate in-game, like 60hz, Gsync seems to turn off and the game tears. I seemingly have to keep it set to 120hz, which locks me out of YUV422 10bit at 4k due to HDMI 2.0 limitations.
The alternative is to create a custom resolution of 63 or 65FPS which the C9 and CX have no problem doing and that way your frame cap is 60 or 62FPS.
Read here about how to properly set up Gsync.
As is without a frame cap, games are bouncing over 60FPS and running out of Gsync range which is why you're seeing periodic tearing. Also, LFC works fine on the CX with Gsync as reported else where using the Nvidia Pendulum demo.