for me I use an external monitor and I use at the same time SwitchResX to turn off mac's display but when I turn on Mac's screen (retina) I notice the same problem even if all the time I use external monitor ....
did you turned off the Mac or just the screen ?
for me I use an external monitor and I use at the same time SwitchResX to turn off mac's display but when I turn on Mac's screen (retina) I notice the same problem even if all the time I use external monitor ....