If you have the newer Roku Ultra (4800/4801/4802) models, try disabling the Auto Power Savings feature and see if that resolves the issue for you. Has reportedly caused some HDMI issues. (loss of communication).
Settings/System/Power/Auto Power Savings/20-min [Disable]
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941