I am using mac os Sierra 10.12.2 and Lightroom CC 2015.8 now, but long before I upgraded my os to existing version I found that while I was using my mouse (Logitech G602) to adjust tone curve (directly drag the curve) in LR rather than using the trackpad of my MacBook Pro 2015, I can't get correct responding.
I am wondering if this is a compatibility issue because I had no trouble when I was using LR CC 2014 with the same hardwares.
Have you tried updating the drivers for Logitech G602 according to mac os sierra(10.12).
So far there's one issue with tone curve after the latest update, refer: Lightroom CC 2015.8: Tone curve still broken in | Photoshop Family Customer Community
My G602 works very well with Lr in Windows-10, including tone curve.
Accuracy is great, buttons can be programmed (Grid view, Loupe view, Develop module, etc) even multiple key presses.
Have you set DPI sensitivity in the Pointer settings?