Hmmm. Try manually setting your display type for your TV in Roku settings and then the System Restart again. First try setting to 720p, then 1080p and then 4k if applicable. Essentially, do not use Auto-detect.
Also try on different HDMI ports and see if issue follows each port.
Sometimes helpful to take to another TV as well to perform this setting change if available.
If able to, post a screenshot of what you are experiencing, but I am pretty sure of what you are seeing.
You can also try using a different wallpaper during troubleshooting to see if that is a culprit as well.
Personally, I would try Factory Reset again and manually select the Display Type during the setup. Usually I set up the TVs in 720p mode and then adjust accordingly later.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941