For what it's worth, I'm having the same issue. Together with a myriad of other issues I've had to wade through. Which I'm not fully confident are fully fixed. But I also have an RTX 2070. Also, my computer screen often flashes to black while running the Oculus app.
I am working through the same problem. WIll work for a few seconds, then black screen. Unplugging the mini-displayport adapter and then plugging it back in gets it working for a few more seconds. I will try updating windows and see if that happens. Running a gtx 1070.