Raytracing

I am using Rhino 7 WIP Mac. Can anyone tell me why raytracing works sometimes and arbitrarily sometimes not? Example, I am working on a drawing that I wanted to get an idea of certain textures and when I click RT becomes very bright but the rendering doesn’t take place. This is not a new problem for 7, it also happens in 6.

gonna need some more detail to be able to help here-

file, machine set up, screen shots, is it every file or just one, using blocks, imported data, old file on new version of rhino, from another render engine, plugins, etc…