There is a possibility the blame lies with the tv rather than the Beam. Sometimes an update gets pushed to the tv and it resets the audio settings. Have you checked (a) the tv is up to date on release config; and (b) that the audio out settings are correct? 

I have exactly the same issue. About 2 days ago the audio from the tv just stopped coming through the beam. I've unplugged it from the sonos and the tv though haven't done any reboots with it or my broadband.

I've since plugged back in and it works for about 10 mins and then drops again. This has happened twice  now since the first drop on Saturday. 

Had the beam since 2019 with no issues. Is this connected to all the updates Sonos are currently doing? Really frustrating as I have a beam and 2 surrounds plus a mini sub. Seems like Sonos doesn't have the reliability ot used to.

Thanks nik9669a, I’ve made sure the TV’s OS is up to date, but I don’t think that could have been the problem since I otherwise don’t have the TV connected to the network. At the time the beam stopped working through ARC the TV wouldn’t have been able to do an update. 
 

matt4566, it is a bit disappointing. I’ve been waiting for a reply to this very issue from Sonos support for a few weeks now. It’s unfortunate how difficult it is to actually contact support. 

Since the iOS device isn’t in the middle of the connection between the TV and the Beam, it seems hard to believe the issue is with the app. Have you submitedt a system diagnostic within 10 minutes of experiencing this problem, and called Sonos Support to discuss it?

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

I’m inclined to follow the thought process by @nik9669a , and check other things, such as rebooting the TV and the Beam, and reseating the HDMI cable at both ends. I’d also want to be sure that the TV is up to date, along with the Sonos system, most specifically the fir ware on the Beam, since the iOS app is only a remote control, or a ‘window’ in to what is happening in the Beam. 

Thanks Airgetlam. I'll have a go at following the steps above at some point and see if that resolves the situation. 

Hopefully this is a blip! 

I’m sure it is, or there’d be a lot more threads starting! Good luck

Was your system set to auto update? There was a speaker firmware that dropped last week… so if that got automatically installed, perhaps that is the catalyst. The about my system in the app should show what firmware level is on the speakers? 

Hi Ian_S,

Do you know I haven't a clue! But now you've mentioned I'm going to take a look. 

Thank you for the heads up. 

Exact same thing happening to me

Right, I’ve actually managed to resolve this.  
 

I did chat to Sonos over the phone in the end. At this point it’s a shame there’s no either callback, or email option for support, waiting for ten minutes isn’t ideal. That said, the chap on the phone was great, can’t fault him. Really wanted to help, knowledgable, and had a lot of resources his end, clearly, to help diagnose all sorts of setups.
 

In the end we managed to get this working on my _second_ TV which did at least verify that the bar’s ARC wasn’t entirely toast. This did give me an idea though what the issue might have been, since he first asked that I disconnect all devices (including my Apple TV) before reconnecting to the second TV. 

After the call, I decided to try the same with my primary TV. I disconnected all HDMI devices, then reconnected just the sound bar, and after a little bit of waiting for everything to handshake, bam I was getting audio through HDMI ARC. 

Tentatively reconnecting HDMI sources suddenly the audio cuts out. Specifically the relatively cheap cable from old gaming PC situated in the slot next to the ARC slot. 
I’m guessing the issue I have is either some sort of electromagnetic interference through the HDMI cable itself, or perhaps electrical interference through the panel. Either way, it was somehow enough to dupe the soundbar into thinking ARC wasn’t available and/or preventing the ARC signal (despite video signal from the soundbar’s HDMI being unaffected). 
Ultimately for me, using a better shielded HDMI cable seems to have largely fixed it, although it’s early days yet and whilst I’ve not seen it, my partner’s had the audio cuts out still briefly. 
Either way, I hope this helps someone else consider if a poorly shielded HDMI cable could be at fault.