Recently my Roku Premiere HD 4K HDR box defaults to the SD version of the HD channel I select from the ‘Last Watched’ menu. Example: CBS-HD is channel 713 in my area. When I click 713 from the ‘Last Watched’ menu, it automatically brings up channel 13, which is the SD broadcast of CBS in this area. The box continues to receive HD, but I have to go to the ‘Mini Menu’ and scroll to the HD channel manually which is becoming a real PITA. Anyone else had/have this problem?
Since that's something within a specific channel/app, you should contact the channel provider so they are aware of it. You didn't identify what channel/app you're using, so I can't suggest who to contact.
Xfinity is our cable provider. The issue started about two weeks ago and is happening on all 4 of our Roku boxes.
That channel is under control of Xfinity. You have to contact them for issues with their channel. Roku has no control over how that channel functions. Comcast has called that channel a beta for years, and it shows.