System Information:
Operating system: Windows 10
Graphics card: Nvidia Geforce RTX 2080Ti

Blender Version:
Broken: Blender 2.93.0-420f538fadfd-windows64
Worked: Blender-2.92.0rc-windows64

Short description of error:
Material not updated in viewport render of Cycles when made a single user (while rendering with OptiX?)

Exact steps for others to reproduce the error:

1. Create a new scene and change the render engine to Cycles (and change compute device to GPU Compute/OptiX?)
2. Select the default cube and duplicate it a few times (Shift + D and move it).
3. Enter rendered viewport mode.
4. Select one of the cubes, and navigate to the Material Properties tab in the Properties window and click on the Make single user button.

5. Attempt to change the materiel by doing something like change it's colour. Notice how this is NOT reflected in the viewport. This is not the case with older versions of Blender.

Here is a screen recording of the issue.