Apple TV 4k stopped decoding 5.1 Dolby over HDMI.

Apple TV 4k SN YQn041163WG OS 18.6.

This unit stopped outputting decoded 5.1 audio to my Sony STR-DH510 audio receiver within the last few weeks. I've checked all the settings and nothing changed over the setup that was working.

I've followed some advice that I found on the web changing audio settings from auto to 5.1 and back with no change. Is there something wrong with a recent software update? In my experience that is usually the problem.

Any help would be appreciated.