i'm not sure of exactly what i do when it happens. at this point, the problem is intermittent and seems to occur randomly. i have noticed that it is more likely to occur after i've shot for about an hour which might represent about 5 GB or so of images. i don't know if that has anything to do with the issue. i am gonna shoot several basketball games tonight and i'll fiddle with the camera to c if i can find the combination of buttons that i might be pressing to trigger my screen to go blank. by the way, i can still shoot even though the screen goes blank. plus, taking a shot seems to reactivate the screen. canon suggested that i might be trying to access the LCD to view an image while image data is being transferred to the CF card (i use a lexar 600x).
the other thing that is weird to me is that i have a canon 1D mk4 that i shot with for years and never experienced this. i can't make headway with canon about the issue until i can figure out a way to repeat what is occurring so that they can duplicate the problem with their tech support.
it may be that i accidentally press the set button or the quick menu button or the toggle button before pressing the playback button. i don't know why that would trigger the screen to go blank, but it might. in any event, i'm not sure of what i do to cause this to happen, but it occurs once or twice each time i shoot. it may even be a software glitch. plus, i access the LCD 100's of times during a sports shoot with no problems.