So I am getting a totally reproducible bug in Premiere Pro CC 12.1.2 (Build 69).
I have a graphical bug to do with the Essential Graphics Text causing the Canvas Viewer to go black. Sometimes the entire timeline goes, and sometimes just the Essential Graphics Text, and it happens when I attempt to change the contents of the text.
I do have a bug with an alpha and an adjustment layer with a video limiter above the text layer, but with essential graphics I continue to get the whole screen going black.
The only way to get it back is to restart premiere, and it will happen again later, though not always.
This is on a MacPro 5,1 with 32 GB of RAM and a GTX 970 with 4GB of RAM.
It is especially frustrating when combined with having to render audio to see multicam audio every time I restart.
I have posted this at Adobe User Voice.
I got a response and they seem to think it is the video card, and graphics drivers. So they lay it at NVIDIA’s feet. And they had me try to see if it happened with render set to CPU, and I tried to see, but it was literally so slow that I could barely function so I gave up after an hour or so.