Hope this helps some folks. MacBook (Retina, 12-inch, Early 2015), Sierra 10.12 Public Beta (16A238m) On waking macbook, backlight would come on, but no video on display and system appeared unresponsive. I tried removing a number of startup items, but the problem remained. Eventually I found this article, suggesting some non-apple display drivers could be a problem - https://www.reddit.com/r/apple/comments/4rrx0s/duet_display_may_prevent_macos_sierra_from_waking/ Code: $ kextstat | grep -v com.apple Index Refs Address Size Wired Name (Version) UUID <Linked Against> 112 1 0xffffff7f80c66000 0xa000 0xa000 com.avatron.AVExVideo (1.7) 7F642CAD-514F-3539-9DF1-A36ABDC91352 <73 5 4 3> 113 0 0xffffff7f80c70000 0x9000 0x9000 com.avatron.AVExFramebuffer (1.7) 9B4554BB-E74F-3571-9C60-1FE38DAFC865 <112 73 5 4 3> I did not have Duet Display installed, but I did have Avatron's /Library/Extensions/AVVideoCard.kext and /Library/Extensions/AVFrameBuffer.kext. These are apparently part of an iPad-as-second-display utility. Removing them and restarting solved the problem.