I have a Roku Stick + and Vizio TV. I bought my Roku a year ago and it has worked fine until my last system update to version 9.4.0 Build 4190. Now when I am watching Netflix and switch over to the Amazon Prime app, the sound goes out. It also happened when switching to You Tube.
If I restart my TV, the sound comes back on but I need a permanent fix. I have also done a Roku system restart and that worked temporarily as well.
I have checked my channels and they are all updated. This problem is still occurring.