I use Sierra on my Mac Pro for a couple of months now. I use the nVidia webdriver for my Geforce 980. Sometimes, after I wake up the Mac screen, the monitor remains black for nearly a minute. I only see the cursor after a couple of seconds. I never had it with Yosemite and High Sierra, but I don't use the latter very often. This bug seems to be related to Sierra. Does anyone have the same experience?