Had you read my post you would know...
1. Does the issue only occur on a specific channel or all channels on your Roku device?
720p broadcasts such as ABC, ESPN cause the issue.
2. Can you please provide the steps to reproduce the issue you are experiencing?
I did this for you by rebooting the Roku Ultra, immediately going to a 720p channel and all looks fine - temporarily - until I switch to a 1080p channel such as CNN or NBC (which is fine at 1080p) and then switch back to a 720p channel and it is queered out and pixelated.
3. Have you tried using another HDMI cable or with a different HDMI port to see if the issue persists?
The HDMI cable/port can't possibly be the problem since it always looks good after Roku is re-booted to a 720p channel. But yes, I switched with no effect.
4. What troubleshooting steps have you taken so far to try to resolve the issue?
See my procedure in item 2 above.
5. Have you removed the channel, restart the device the add the channel back?
Yes and since Roku automatically updates/checks for YouTubeTV software daily, this is redundant since the latest version is always present.
6. We recommend starting here to troubleshoot any channel playback issues: How to resolve a channel playback issue
My Roku is ethernet wire connected to my router (no WiFi), there is no issue with connection speeds. What appears me is that the Roku does not automatically adjust the 720p signal to correctly upscale when the channel is changed from a 1080p channel. As I've stated, the Roku and YouTubeTV 720p upscales correctly only after a system restart, thereafter any change to 1080p channel and then back to 720p is bad.