Hello, this problem might have been addressed before, but the keyboard on my 2013 iMac usually has issues after waking the computer. Buttons either do not work, or take a few seconds to appear on the screen, while some will repeat infinitely until I restart the computer. This only started when I upgraded from Yosemite to El Capitan. I keep hoping that each new version of El Capitan will fix this but it doesn't. Does anybody have suggestions?