My ROKU was returning to the home screen after 3 minutes on any channel.
I had recently disconnected and reconnected the HDMI cable.
I re-seated the HDMI again and the problem was gone.
It seems that the HDMI connection on a ROKU is very touchy both at the ROKU and TV.
So.. if there is any strange problem with a ROKU try re-seating the HDMI cable with a firm push.
A TV on a swivel mount can loosen the HDMI cable after a while.