Here's my take. Spectrum sold me a killer deal on internet+home phone+streaming channels, so now I'm on my third day of the Roku. The Roku streaming stick 4K is on HDMI3 of 32" Vizio, with power from wall plug. (The Roku updated itself upon installation.)
Today, for first time, I noticed a frozen image of the final frame of a JibJab.com commercial, while audio from selected channel on Spectrum was playing. I noticed that changing to the adjacent Spectrum channel unfroze the video, and changing back to the first channel the video was also good. Within an hour, there was a frozen image of the final frame of a Target commercial, and the same channel-change sequence had to be used. My impression is the freezing commercials are from Roku, not Spectrum, and that there is a defect in the release of the video stream that carries the commercial, which is preventing the Spectrum video from starting.
Thank you all who have posted. From this, we know this is a long-standing unsolved problem. Is there a way to know if either Roku or Spectrum is working to correct this?