I have the issue with CBS local channel in South FL on Roku Model 4620X, it only happens in the early afternoon and into the night. Frustrating that I have to go to the Over the Air Channel to watch.
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Please be noted that if you occasionally see poor video quality or rebuffering, it may be due to temporary network congestion.
There are a couple of things you can try to resolve this issue.
Keep us posted from there if you need additional help.