I have 3 Roku's and 2 of them have problems with the sound going out. I used to be able to unplug and then replug and it would correct the problem. The sound went out yesterday and unplugging didn't work so I plugged my headphones into the remote to see if the sound worked that way and it did. By accident I pulled on the headphone plug making the plug come partially out of the headphone jack on the remote and the sound on the TV began working again.
Perhaps these problems with sound are related to remotes that have a headphone jack.