It is a overheating problem. What is going on, for I can fix cards this way that the display quits working, is just like the old Xbox 360s fats, the gpu/cpu solder is crap and pulls away from the board and as your card heats up the chip pulls away and doesnt make contact anymore, causing you to lose display. The fix I been doing for video cards, amd and nvidia, is I use a heatgun and heat the sucker up, making sure its on a flat level surface, and heat it up really good making it flow the solder again, and then cool it down, re paste it, and fixed. Ive been running a AMD RX 580 in my sons pc for a while now with no more issues and gets used every day for hours. Last one I fixed was a GTX 970 with it coming on, no display, fans spin, heated it up with my gun, and it fixed it as well. I used to fix 360's back in the day with the x-clamp and my heat gun with almost 100% success, though some just didnt like to re-flow no matter what.
And yes I know there is a way to do it with the oven, but I dont like to have to buy a seperate toaster over to do it with, and then have to remove all of the plastic bits as well to do it that way, and Ive been doing so long with my gun I havent come into a problem, well I shouldnt say that for I did it to the Onkyo TX NR809 that has the same problem with its DTS chip desoldering from the board, heated it up the first time, lasted about a month, then redid it, but like a idiot, wasnt thinking right

, while hot and still liquid I touched the chip causing all the solder balls to squish and now need to get a new board for it
But if you have means to a heat gun, give it a try and should fix it for you.