Thanks for your suggestion. Since my posting I had to do a Roku factory reset to clear the problem.
My guess is the Voice Remote Pro got confused at some point because just before the Roku crashed I was getting responses similar to "that feature/function is not yet available". After several of these it crashed...thus the scattered pixels. Since the full factory reset was performed it has been working fine.
I hope this post may be of some help to others in the future.
Regards,
Getaclu