trouble waking from sleep
I have a brand new fall 2015 27 inch retina imac with fusion drive, running OS 10.11.2
After a month or so of use, a problem developed. If I put the computer to sleep, and it stays asleep for a long time, it has difficulty waking up from a keyboard or mouse button press. The screen turns on, but items are missing from the desktop, and then the screen flashes gray with a graphical glitch in the upper left hand corner and the computer goes back to sleep.
Usually if this happens the computer will wake normally the next attempt. Sometimes I have to try several times. I've tried resetting the SMC and the NVRAM and trashing the power management plist. None of this worked.
iMac, OS X El Capitan (10.11.2)