This one is a bit complicated. I have a LG UR8000 TV, Google Chromecast 4K, and Sonos Beam (Gen 2). This week I tried playing the new Lord of the Rings episode and I had no sound. I finally figured out there was a slider to disable Dolby Digital Plus. Once doing that the audio was working, with surround sound, but the Sonos app said PCM Stereo. Before turning off Dolby Digital Plus there was no audio showing on the Sonos app. I never had to turn off Dolby Digital Plus before, thought maybe Dolby Digital Plus is a new option.

I am using passthrough bitstream eARC on the LG TV with the Chromecast 4K. I am casting the show from my mobile phone. The Chromecast 4K shows in the settings Dolby Digital Plus is compatible and enabled. PC connected on another HDMI port plays Atmos videos without any audio issues.

Prime Video settings are set for Best quality and unlimited data. Also have the Ad-Free tier subscription.

Updated Sonos speakers to 80.1-56190 and the issue still persists. TV is up to date. Chromecast 4k is also up to date.

Anyone have similar issue? Thoughts on what might need changed?