Hi, I'm just surfing the web when it occurs. It occurs unexpectedly.Are you running a video at full screen or something? You said it happens at least twice a day, I'm curious to find out what it is you're doing when it occurs.
I wish I can do that so easily.This can be hardware failure of your screen, take it to your local apple repair shop and ask them what might have caused this.
I'd never seen it before. I'm going to submit the case to Apple, I hope they could fix it as soon as possible.Wow that's pretty bad. You've never seen that before you upgraded to El Cap 10.11.5? It may be a pain, but I would definitely submit a case with Apple for that...they really should see that.