Registered to say that I've had the same screen flickering problem with my Galaxy Tab Pro 12.2 wi-fi tablet. I have actually returned two and am hoping for better luck with the third. I've bought all three from Costco in Phoenix, Arizona. With the first, I used the tablet for almost two months before the screen started flickering and I got random shutoffs/reboots. With the second, I got these same symptoms within two days. The flickering continued after a system restore, so I don't think it's a software problem.
Elsewhere on the internet, people have reported flickering while watching video and fixed it by turning off software rendering in developer options. That, however, seems to be a separate problem. I experienced the flickering during all activities, and changing the rendering setting didn't fix it. Nor did turning off auto-brightness.
The flickering seemed to show up most often when the battery was low, making me wonder if it was a power problem. I've also noticed, though, that the tablet seems to get really hot around the top center, where the camera lens is, especially on the backside. This makes me wonder if the tablet is burning itself out, or if using a case might hasten the problem by holding in heat.
Bought this third tablet from a different location, thinking maybe there was a bad run or something. If anyone figures out the issue or gets any kind of useful response from Samsung, please post.