Lately when i start watching a show -regardless of whether it is netflix britbox acorn etc., the show will run for about 15-20 mins and then the roku goes back to the main menu? WTF.
See if Roku's power savings feature is the culprit. If available on your device, it will be located under Settings/System/Power/Auto Power Savings/20-min inactivity.
https://support.roku.com/article/6306527767575