I searched for "Power-Only Mode" and got many links about LG TVs. For example, one said it came up with he used the volume control on his Apple TV. Others weren’t specific about how it happened, but I didn’t happen across any posts mentioning Roku. One poster said you need a “service remote” to deal with that screen. As such, I think it’s an “LG thing” and you’d be better off asking in an LG forum.
The only other “generic” suggestion I could make is that maybe re-setting up the remote for the TV and selecting a different LG code might avoid the issue/feature.
