In my case, I also use DaVinci Resolve (the free software).
In my case, I am using R9000P, it come w/ Lenovo Vantage, when I am doing some editing / export the clips, the VRAM bar will go up (I think refer to it use up the VRAM), the "black screen" will come out! And it is quite consistent! (i.e. normally, it won't come until I do the video editing).
So, I guess the VRAM might not enough, I am not too sure if I add extra RAM (currently 8GB x2) will help (e.g. change to 16 GB x 2 = 32GB)