OK, I HAVE FOUND THE CULPRIT, OR AT LEAST A CLUE.
At least, on my machine. I have been installing and uninstalling various versions of windows, vray, and AMD drivers. There was no magic bullet. I went back to square one, removed the AMD drivers (they have a clean uninstaller program), and reverted to V-Ray 3.6. However, I’m not sure any of that really matters. FWIW I am running a bootcamped 2016 imac, which always throws some more fuel on the fire.
The cropping issue in the asset editor goes away when you change the scaling resolution for the monitors. If they are both set to 150% … there is no issue. Weirdly, it does not seem to work at all scalling resolutions, but it does work when both are set to 150. However, this means your programs are huge on one screen, and tiny on the other. Which is not really a solution, but it is an explanation, which helps me relax a little.
Good luck everyone.