This is the first thread I have posted in here and I hope someone has the same issue can reply. After updating to High Sierra for about a week, I realized that the screen brightness did not respond to the change when I move the brightness slide on the touch bar. Neither did it respond to change on the brightness in System Preference. Even worse, when I close the lid and reopen it, the screen did not turn on. Resetting the SMC and NVRAM did not help solving the issue. After playing around with the setting in System Preference, I found out that if I turn off the Automatic Graphic Switching option in Energy Saver, the issue goes away. My guess is there is something wrong with the integrate GPU because turn off the Automatic Graphic Switching means the computer will always use discrete GPU. So I brought my mac to genius bar to let them running the diagnos software and it turns out there is nothing wrong with the hardware. They also tried rebooting into MacOS from their server, which is running the old version of MacOS, and the brightness changing is working. Therefore I believe it is a software related issue. If anyone happend to have this issue and fixed it, please let me know how you fixed it. Many thanks!