Some Roku devices has a power setting that puts the TV in a low power mode, very similar to many devices "off" mode. Settings > System > Power
Again, not all devices have a setting such as that, but for those that do, turning the functionality off may make the Roku respond to app based remotes better.
Also, be aware that if your Roku ever disconnects from the network, or if you change your network, you will need a physical remote to reconnect to the network. You cannot use the app to set up a Roku device on a network.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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