About to throw my Ultra in the trash, drop all of my Roku subscriptions, and get an Apple TV or Chromecast.
When changing apps, or changing channels within an app, or going into or coming out of a commercial, the audio drops out and I have to turn the TV off and back on to get audio back.
This has been happening for years. It doesn't have anything to do with the app being used or audio settings [Dolby, standard stereo, etc.] or equipment [TV speakers, soundbar, etc.], or not updating software.
This is a Roku software and/or hardware fault and they know about it. Either the engineers can't figure out how to fix the problem or they have determined that the fix would be too costly and not enough people are complaining about it yet.