When I use CPU everything works fine, but when I switch to GPU all materials using Principled BSDF or Glass BSDF shaders go completely black in the viewport rendered view; all other shaders seem to work fine. I am using Cycles in blender 2.83 and my graphics card is a GeForce RTX 2060, which I just updated.
$\begingroup$ No info about render engines and shading modes the issue appears in. Try to set materials blend mode to Alpha Blend instead of Opaque in the material settings. Render engine should be set to Eevee for this option to appear, but those settings should also affect Material Preview shading mode back in Cycles. Also if you use Cycles try to increase Transparency samples in Render Settings -> Light Paths. $\endgroup$– Andrey SokolovAug 30, 2020 at 6:47
$\begingroup$ @AndreySokolov my apologies. The problem only appears in Cycles; works fine in Eevee. Increasing the transparency samples didn't help, and the Material Preview shading mode gives the best results with the Opaque blend mode with both engines. $\endgroup$– Natalia KownackaAug 30, 2020 at 11:03
I don't know if you solved this, but I had a similar issue until I realised that I had Transmission Bounces set to zero (not Transparency bounces as mentioned in your comment above) ...
$\begingroup$ It's been a while since I posted this, and I don't remember how I solved it. However, the exact same problem appeared just a few days ago, and a simple PC restart solved it. I'm assuming the same thing happened last time. $\endgroup$ Apr 6, 2021 at 17:23