Installed El Capitan Beta 10.11.5 a few days ago. I noticed just the past couple days that I would try to wake my rMB from sleep and it would wake. I tried to restart, hit space bar, escape, type the password, etc. Nothing. Just a black screen. I discovered that if I plug it in and then hit the power button a few times and swipe the trackpad a few times I'll get the password screen and can proceed from there. It's bizarre and FRUSTRATING. I checked the support forums and found nothing similar. rMB 1.2 512SSD. Early 2015 - no other issues than a shift key that does not depress. Any advice is appreciated - even it's just that you are seeing this too!