if you read most of these comments you will see that for many this is a daily problem.
For me, we have changed HDMI cables and inputs, system restart (at least once a day), unplugged the roku, tried changing audio settings to stereo. This is only a temporary fix.
Sometimes it will happen when going from one app where sound was working to home screen then to another app where immediately no sound. Sometimes we will be watching a show/movie and all of a sudden no sound. I have had it happen within Hulu, Prime Video, YouTube and Netflix apps. But in ALL occurrences when I go back to home screen to do the system reset, I hear the “thunk” that roku produces with each move of the cursor/selection. So the roku is still sending sound thru the HDMI cable to the TV, it is just being selective as to which sound it will play.
Please fix as this is annoying that we must restart daily and has been happening for months now.