You bloody legend, I need to do a bit more testing but I think this is it. I’ve not messed with this option for yonks (and like I said, it’s specifically advised against in the recommended G-Sync setup) but my theory is this:
- Zwift appears to use vsync with triple buffering by default.
- Enabling G-Sync seems to override Zwift’s own designed behaviour.
- You end up with a sort of hybrid; even with vsync left at the default of ‘Use the 3D application setting’ (ie let Zwift decide), adaptive sync does work but with some legacy vsync characteristics, like a refresh rate cap but also my 50% frame rate issue.
- G-Sync on with vsync off introduces tearing, so it does need to be turned on one way or another.
- Forcing triple buffering on manually in NVCP appears to reset those vsync characteristics, meaning the cap is still there, no tearing, and no more sticky vsync. Best of all worlds!
Happy days. Gonna try it out a few more times before I mark this solved and update the OP. Thanks Steve!