I am using a pretty recent build of Houdini and I seem to be encountering a similar issue to this post from a year ago [www.sidefx.com]
However the solutions proposed don't seem to work for me. In fact, even without a Dome Light I still get the same difference.
I am using MaterialX and no Normal maps. It's a pretty basic setup but the XPU version seems to show a more faceted version of the mesh and not smoothing regardless of what I do with the normal attributes. May not be related to Normals and it's a Shadow issue instead?
Am I missing any setting by any chance to get it working with XPU?