No Audio coming from Amazon Prime and Netflix app. Youtube is working fine. I did restart, delete and installation of app as well and it didn't work. These apps are working fine on my Fire stick no idea why they are not working on ROKU.
The same happened with my Roku Premiere with Amazon Prime. I had to adjust the stereo output mode setting of the Roku itself. It helped on mine. Amazon Prime audio worked consistently after the change.
Choosing From the Roku Home screen, select Settings, Audio, and Audio Mode. Choose a different one such as stereo and see if it helps. Accessing the menu could be slightly different depending on your device and age.