I’m trying to tell what the difference is there and I think maybe you have the Denoiser post effect on in v8 but not v7. Click the little star icon at the bottom of the Raytraced viewport to toggle whether post effects are used. You can also check the same icon in the Properties panel when that view is active and nothing is selected to disable Denoise if that is what it was. It’s not AI
That looks like a meshing issue to me. Reduce the problem to a single piece of geometry, and zoom into that. Or there is a marginal far-from-origin issue?