I don’t see any earlier posts about your problem, so could you be more specific on “seems to happen when watching anything except live TV.” With so many apps on Roku, people have wildly different definitions of “anything” on Roku. (Sometimes “anything” turns out to be any channel within a single app.)
I have seen some apps that are buggy and they can cause a random restart or a jump to the home screen.
Also, if you want to check for hardware defects, I’d suggest a Roku Express or Express 4K. These are cheap and much easier to buy and move than TVs.
Banned but back. Because why not?