This seems to be happening quite frequently to me lately, and it makes it very difficult and frustrating to work. Seemingly out of the blue all of a sudden any changes I make to a material in the node editor do not change in the viewport render until I either toggle out/in of render mode, or click certain tick boxes in the properties dialog area (like texture space, or UV related options) and this behavior sticks with that given object through new materials, saving, and restarting Blender. It also remains for that object whether I change it to an Uber shader or Principled BDSF. Yet if I use the Principled, I can switch to Cycles and it updates on the fly just fine, until I switch back to ProRender in which it still won't update still. So other than re modeling the object I am kind of stuck re-starting the render view EVERY single time I adjust a shader or anything. I have tried, and confirmed that this behavior is the same in both Blender 2.81 and 2.82. Here is one simple scene to show you the issue, it's the object named "Problem" with the material named "Problem" also.