Roku worked perfectly almost a year. Last night the audio did not work. It is not the TV set. I changed input to antenna and it blasted loud an clear.
I only had mine (model 3810X) 2 weeks and the same thing happened. Moved the input from HDMI1 to HDMI2, no change. Unplugged the stick from the TV and removed power. Waited about 10 minutes, inserted back into HDMI1. Audio restored. Hopefully this won't become a habit.
I should have posted the answer long time ago.
1) navigate to settings
2) navigate to system
3) select "System Restart"
Restart your Roku device.
That's it. Sound works again.
Note: For those as old as I am "Hi Yo Silver, away"