Hi @BrianJ,
A late reply (holidays), but I am still struggling with this issue.
There is no duplicate geometry, and it unfortunately affects every simple shape.
I found this thread, describing the same problem for an earlier version of Rhino (my version is 7 7.9, up to date): Problems in shaded and rendered view: dots everywhere
The command to fix it, is unfortunately not known in my Rhino version.
What can I do?
Thanks in advance,
Stella