The only change I just made was to completely disable the TV speakers. Maybe that will make a difference. The rest of the settings were as they are pictured.

Try disabling System Standby too since you don’t have any other devices connected.

I was just going to update this because my sound just dropped! The diagnostics is a waste of time.

I'll look at standby

Ok. eARC is the only thing on. Let's see how that goes.....

If that doesn’t work, one other option would be to change the S/PDIF and eARC setting to Dolby Digital Plus. I’m not sure how this will affect non-DD+ audio though.

So, I realized the hdmi port on my TV is ARC but not eArc so instead of leaving the audio compression set to auto on the sonos, I changed it to compressed. It seems to be better but it still will drop, l but very in frequently. 

I am thinking about putting it on the optical cable to see if that takes care of it but it's pretty aggravating to have purchased a PRICEY eArc atmos compatible sound bar and then not be able to receive that format.

Didn’t the latest firmware update for your TV add eARC support?

I’m having the same problem with my Arc and submitted multiple support tickets with no solution in sight (Sony X900H). 

based on this thread, it seems like it’s a problem with Sony, which is funny because this does not happen with my PS4, only with built in streaming apps. I can’t remember if this happened with my old Plasma but my wife is ready to throw the TV and Arc out the window.