Same problem here…

LG C2
Beam Gen2, Sub Mini, 2 x One SL
HDMI 1: Apple TV (Gen2)
HDMI 2: Beam 
HDMI 3: PS5 (currently set to 7.1., for no dropouts…)
HDMI 4: Switch (annoying dropouts… sometimes even NO sound)

My Apple TV is connected with an HDMI CEC Blocker. But i am using mostly the TV Apps. 
Playing around with connections and power cycles and suddenly it was working.
PCM 5.1 was running without issues for about 6-7 weeks.

After a Sonos Update dropouts again…
Trying around with power cycles, Ethernet/wifi connections, settings and unplugged HDMI 1.
Working again with no dropouts.

Sonos Update yesterday… Dropouts…

HDMI 1 has the same dropouts! Not only HDMI 3/4.
In the Sonos App „PCM 5.1.“ is disappearing for very short moment when the dropout accurs. 


Only stable but not acceptable „workaround“: don`t use Apple TV, PS5 7.1 Mode, Switch Stereo Mode.
 

LG C1 here. I had the issue on HDMI 1 and 4 with a PS5.

I disconnected every other HDMI (except the beam on HDMI 2 and PS5 on HDMI 1), unplugged the power from the TV and PS5, waited for a few mins then powered them on again and that got it working fine for now. I hope it stays that way until a proper fix exists.

LG C2 and having pcm 5.1 dropouts from PS5 in HDMI 3 and 4. Moved PS5 to HDMI 1 so far no dropouts. Having contacted LG support bout this issue and this forum, I have had LG response:

"I am just getting in contact as our Technical Team has responded on file and have advised that there are no differences in the HDMI ports and so there should not be any reason as to why HDMI 3 and HDMI 4 would be different to HDMI 1. They have advised that we can book this in for a repair as this could be an issue with the HDMI 3 and 4 ports themselves."

So am now booked in for HDMI repair. 

Waste of time IMHO, your TV behaves exactly the same as any other LG TV of its model.

It works “as intended”, the problem is that the “as intended” is faulty.

It almost seems to infer that the LG Technical Team are aware of a hardware issue with that TV model. I would have the repair and just see what happens after that.

No don’t try to pawn off the issue to LG lol. It’s a Sonos issue as well, clearly.

It really doesn't, but agreed, if LG are willing to commit some visible effort into trying to isolate this fault then worth pursuing. If they have prepared a h/w HDMI fix for C2, don't fancy the chances of it being back ported to C1/CX.

Will give the LG repair team a chance. As it is strange that the 5.1pcm works fine on hdmi 1 for the last week where in hdmi 3 for the last 3 months I've had to resort to 7.1pcm as the pauses in 5.1pcm have been very annoying.  Had the same on hdmi 4 but only tested for a few hours but it was immediately stuttering.

Yeah, I wouldn’t read too much into it either. Probably just a standard response from local LG support. As you are under warranty, they are willing to take a look at your TV. They probably don’t even know that this an issue specific to the Sonos Beam Gen 2 only.

If it’s home service, then you’ve got nothing to lose. But if you have to send the TV to them, I personally wouldn’t bother as it’s a high risk (they could damage the TV), low reward play. In my country, repair is limited to basic diagnostics and part replacement. They don’t tinker. Last resort, they simply replace the TV. And I doubt a simple part/TV replacement would do anything.

I’ve been running my ATV4K Gen 3 on HDMI1 for the past 3 days with no issues. Although there have been reports that HDMI1 also bugs out, it does appear to be more resistant. So there’s probably a lot of users who don’t realize that they are actually affected by this bug because they play their content on HDMI1 (it is port 1 after all lol). 

2 days here without issue with ATV4K Gen 3 on HDMI 1. I usually run my set top box on HDMI 1 but with CEC I guess it doesn’t really matter as I never actually have to select an AV. 

Yeah home repair, wouldn't have bothered if it had to go.

When I run the following commands on Raspbian on a Raspberry Pi3 with Beam2 on eARC:

sudo speaker-test -Dhdmi:vc4hdmi -c6
sudo speaker-test -Dhdmi:vc4hdmi -c8

the 11111 menu displays either 'PCM 6Ch 48000Hz' or 'PCM 8Ch 48000Hz' during streaming and Sonos app also shows the appropriate Multichannel LPCM mode. 

When speaker-test is killed, Beam2 goes silent, Sonos app format goes blank immediately, 'cat /proc/asound/card1/pcm0p/sub0/hw_params' shows the RPI’s sound card device is already closed, but:

• HDMI1 (not bugged) - 11111 holds the same PCM mode until a different speaker-test format stream is started, up to several minutes later
• HDMI3 (bugged) - 11111 holds the same PCM mode, but only until the 59th second after the previous dropout, then 11111 shows the format being pushed to PCM 2.0, where it then stays (again, until a new speaker-test format is streamed)

The above behaviour is the same for 6Ch and 8Ch, the only difference I observed being that if speaker-test is streaming 6Ch during the 59th second on HDMI3, the Beam2 audio (as we know) is interrupted for 1 second. There is a 59 second event for both 5.1 and 7.1, but it is only audible on 5.1.

Replacing the Beam2 with an eARC AVR - when speaker-test is killed on HDMI3 there is no drop down to PCM 2Ch at 59s, both formats remain until a new stream is started. This doesn't give any indication how Beam2 is involved, but only its presence is triggering the TV into doing something every 59s. I couldn't find any obvious HDMI events/errors (CEC, handshakes, etc) on the RPI at the 59s intervals.

A post I found recently observes the dropout period is not tied to the amount of content played (back when it was approximately 40s):

https://discussions.apple.com/thread/254365553

If I unplug the HDMI cable after killing speaker-test, 11111 shows HPD/5V/etc drop low, Video shows 0x0I@0.0Hz, but audio still holds the most recent PCM 6Ch/8Ch value. This is the same on HDMI1 and HDMI3, for the RPI and PS5 as sources. The TV is not reporting the audio format on the input wire. Rather, I guess it’s whatever the mode the next circuit in the audio path was most recently configured to based on the the last frame of audio received. PCM 2.0 is only displayed again when HDMI cable is reconnected. On HDMI3, streaming 5.1/7.1 then resumes the 59s timer.

@RANDUSR23296 Damn. Sonos should at least send you an Era 300 for all your work lmao. But thanks to you and @OmriP for zeroing in on the HDMI1 thing. If this lasts for me, I could probably hold off on sidegrading now for a real upgrade later.

I’d settle for Sonos sending me a human readable log of what events my Beam 2 (in my house, on my network) is seeing on the HDMI eARC pins around the 59s window Realistically, having spent a while on Google, the HDMI spec (1.4 and above) is such a trade secret there’s at least one good reason why that will never happen.

@MJW75 really made a break-though spotting the blips on the 11111 menu. I’ve tried pulling the HDMI plug on a 6ch source on my A1 and it immediately drops to 0Ch, so there’s a difference in how that signal is reported between those chipsets. Maybe the/another bug causes this difference, maybe it’s a recent intentional change from LG to monitor this specific issue. Unfortunately I don’t have a downloaded copy of C1 v03.33.11 firmware to downgrade to find out.

sudo speaker-test -Dhdmi:vc4hdmi -c6
sudo speaker-test -Dhdmi:vc4hdmi -c8

Bruh Sonos should be paying you for doing their job.

On another note, the sound drops stopped on their own since I installed the last Sonos update and I don’t know if it’s because of the update or because of some unrelated voodoo. I’ve had this problem for weeks now and gave up on fiddling around because it seemed unlike last time this time nothing I did worked, but yesterday it just fixed on its own, and that was the first time I used the TV since the update.

At this point I’m too happy to power cycle the beam and see whether the drops return or not XD

To be fair, I did think of a scenario where the Beam 2 is blameless: Maybe the TV has a bug that means the first device eARC device it registers (and it does seem to cache the details of eARC devices) is bugged, but subsequent devices are not (it’s not uncommon for first items in software containers to trigger additional logic or follow modified algorithms that subsequent items added do not).

That would give the illusion to a Beam2 owner that it somehow was triggering the problem yet in reality it was still functioning 100% to spec, particularly as eARC devices are still relatively rare and the Beam2 was likely the first eARC device connected up. Testing a different eARC device (for the fewer users who have access) would work fine and look like only the Beam2 was bugged.

However, if this was the case here, I’d expect to see reports on internet about other devices having dropouts, because they’re the first plugged in, but I couldn’t find any. I could (probably) test this by factory reseting the TV and connecting my AVR as the first eARC, but the lack of evidence on my searches suggests this would not be worth the effort.

Also, that doesn’t prevent Sonos support actively help isolate the issue, and/or even giving some sensible technical engagement (I do appreciate @Corry P’s recent update indicating related activity by the community team).

Apple TV 4K 2nd Gen and later support eARC so could be used for testing. I may give this a go if I get a chance later today (my HDMI ports are a real pain to access though).

https://support.apple.com/en-gb/HT207117

I had chance to try that with a HomePod mini - I couldn’t find a way to get it out of PCM 2.0, but admittedly didn’t spend long trying to work out why.

Interesting. What were you using as the source? I was thinking of trying my ATV 4K Gen 2 as eARC and putting my Gen 3 on HDMI 3 or 4, after re-setting the TV.

If this were the case you’d see loads of posts here about people with Sonos Arc, or any other soundbar. The fact that it’s so specific to the beam 2 suggests it isn’t blameless.

I found some of these HDMI breakouts and buzzed out my sacrificial HDMI cable and I did manage to cut (only) pin 13 successfully. Not sure why C1/Beam 2 eARC is so dependent on CEC, it shouldn’t need to be.

In this caseI used PS5 (playing Steven Wilson blurays (remixes and solo albums) - they typically have a choice of PCM 2.0, 5.1, DTS and sometimes ATMOS and the prog rock albums tend to have fewer gaps between songs).

I found Elton John’s Farewell From The Dodger Stadium on Disney+ a useful LPCM 5.1 test on AppleTV. It’s live, >2hrs with no silences, and I’m used to hearing those songs over the years so they don’t wind me up. I can then flick to something like Hamilton for a bitstream/Atmos test.

I will have another go sometime this week using the Raspberry Pi, as that’s actually now the simplest source to flick between formats (now that it’s setup) even if the audio is a little dull...

Update. I’ve had no issues with my Apple TV 4K Gen3 on HDMI 1. But the issue still bugs me because I know the issue is there and could cause issues in the future (i.e. when my son wants to play his Switch on the TV or we buy a PS5). I put my Apple TV back on HDMI 3 and the issue returned instantly, as expected. But, I then swapped the HDMI cable between the TV HDMI 2 (eARC) and the Beam Gen2.

The cable I used is a one way fiberoptic cable. I thought maybe the one way nature might stop whatever the Beam is sending to the TV and interrupting it every 59 seconds….. anyway, I’ve tested for about 1 hour now and it hasn’t had a single dropout. I know this isn’t long, but it instantly started dropping out with the original Sonos supplied cable. I’ll keep it setup like this and will report back when I’ve tested it some more.

Update - 5 hours of watch time on a 5.1 PCM source (my wife is bingeing Star Wars Rebels on Disney+). Not a single dropout so far. 
 

To clarify my previous post, the cable I used is a HDMI 2.1 one way optical cable.