I was just coming back to report the same thing!
I'm dumb, and I was using CKB even though my keyboard isn't RGB.
When I first got my K70, the Option and Command keys were swapped. This drove me nuts, so I tried to remap them in the System Preferences. But for some reason, that wouldn't work. So I searched for a driver and found CKB. Installed it, used it to remap, and it worked great.
With the Sierra glitches, I gave up and put the K70 in my closet. But then I read someone asking, "Do you need CKB if your keyboard is only one color?" Someone said no. But I ignored it because I remembered the key remapping issue I had.
But that had me thinking...I deleted CKB and rebooted. The Shift + Click worked again. Fully functional keyboard, except for the swapped Opt and Cmd. I opened the Modifier Keys settings in System Preferences. I just noticed THERE'S A "SELECT KEYBOARD" DROPDOWN, WHERE I HAD TO CHOOSE "CORSAIR K70R GAMING KEYBOARD"!!!!!!!!!!!!! That's why it wasn't working before.
So my modifier keys are mapped properly. It works great! I'm so happy. I was just about to sell it.