To me it happens on apps run by tvOS (Apple TV 4K) but never on apps run by webOS (LG TV).
Apple TV 4K and LG TV are both connected to 99.9% stable optic fiber symmetrical internet link DL 50 mbit/s UL 50 mbit/s.
Similarly tvOS (Apple TV 4K) does not handle audio format properly and sends PCM for 5.1 while apps for same content provider run by webOS never has a problem to send Dobly Atmos if available or Dolby Surround DD or Dolby Surround DD+ when 5.1 is the only audio available. tvOS requires manual disabling of Dolby Atmos for this to work.
PCM on JBL Soundbar 9.1 sounds like garbled audio. Distorted. Wrong. Useless.
These two cases (internet related, audio related) show that apps on tvOS seem to have issues while apps on webOS prove that there is nothing wrong with my hardware: LG TV and JBL Soundbar 9.1 connected to HDMI ARC port.
LG TV 65SM8500PLA
webOS TV Version 4.9.7-11 (goldilocks2-gyoen)
LG TV > SOUND OUT > HDMI ARC > Digital Sound Output = Pass Through