Try this:

Disconnect everything from the TV and unplug the Arc and TV from power for a couple of minutes. Plug everything back in but keep everything disconnected. Make sure Simplink is enabled in the TV settings. Run TV Setup in the Sonos app and follow the app instructions. When the app instructs you, connect the Arc to the TV’s HDMI ARC/eARC port using the Sonos-supplied HDMI cable. After the Arc has been successfully connected, connect any other devices to the TV.

And set your TV to these settings:

HDMI Input Audio Format: Bitstream
Digital Sound Output: Pass Through
eARC Support: On (If only using the TV’s native streaming apps, it is not necessary to have eARC enabled.)

Thank you.

I am streaming all non-native content through Amazon 4K MAX Firestick, so I understand I will need to turn on eARC support.   The loss of sound is random, usually when switching on the TV or navigating between streaming apps.  Sometimes I seem to lose it when there is no input through the remote for awhile.  I will try your recommendations to reconnect everything.

Can I also ask if it is normal for the HDMI port on the Arc to be very sensitive to any touch / movements?  When I jiggle it even in the slightest, I risk losing the connection to my TV?  Its a brand new cable specifically compatible for up to 8K with eArc support.

Still unclear what is the real cause for loss of sound.  Is it the TV, the Amazon Firestick4K Max or the Arc?   All I can seen to narrow it down to is something drops / is not passed or maintianed through the eArc connections…. However, I don’t seem to have any loss with 2 channel audio, like live sports)  I only seem to lose sound with 5.1 or higher channel processing..