So the release notes have dropped:

In this update:

• Improvements around delayed audio with home theater surrounds and Subs, as well as audio dropouts due to delayed audio.
• Bug fixes and performance enhancements.

the fact that they specifically called it out gives me hope

Yep all good so far. Added tru play and everything is as it should be. 

Interesting ........ Just had to take off and put back on SVC on my Beam Gen 2. Only noticed as I use it to turn on the TV now and when I went to do that 5 mins ago, nothing happened and the light didn't do it's little flash thing when I said Hey Sonos. So I took it off and put it back on in the app and it's ok now. I have not had the issue in this thread given I have a Beam but maybe this suggests they have done something to the HT set ups as they've said? 

How I "think" the echo started, and how I fixed it

We had the echo in our Arc + Sub + 1's x two for surround to create a 5.1 Dolby Atmos set up. Like many others the echo kind of started, but I could not pinpoint a reason. We did a ton of things, including upgrading our ATT router (the arc is connected by lan and our wifi is an Orbi whole home system), which honestly sort of fixed the echo for a good while.

BUT we got the echo back when we pushed content using Chrome cast. We have an Apple TV4k and iOs devices so we always try to mirror/use Apple to push content from a phone. Well, YouTube and Facebook both won't let you push with Apple/Mirror. I assume Youtube does this because they own ChromeCast and Facebook does it cause they want you captive on their platform. Anyway, when we went to push, it borked a bunch of times and SPECIFICALLY started playing audio super loud through the surround 1's then froze. We tried a few more times before finally getting it set up correctly. But then we had not only a single echo, but a double echo. Each of the surrounds we're off, one by 1 second the other by 2 seconds. The navigation beeps on streaming services alone drove me nuts. So, I disconnected the surrounds (something others have said is a fix) and this did fix my issue. But here's a weird bit, when disconnecting the surrounds they each had a different "group or room" which is strange cause I only have one Living Room. In the menu/system it only showed "living room" but when disconnecting the first surround I got a message "disconnect from "Living room 1" & when disconnecting the second surround it said "Living room 2". I disconnected both, then reconnected them to the only Living room available and viola all was well instantly. I did have to redo the TruePlay tuning to get that turned on, but it sounds like it's supposed to with no echo or weirdness.

Of course, there would be an echo if each surround was on a separate but duplicate "room."

I still contend that this is an issue on Sono's side (how does using ChromeCast create duplicate rooms?)

TL:DR Using ChromeCast to push content from Youtube or Facebook appeared to create the echo effect. Disconnecting surround speakers solved it, & when disconnecting the system showed duplicate living rooms

So far so good, but last update it didn’t show up right away.

Hopefully with them specifically calling it out it’s actually fixed. 

I think it could be that the act of disconnecting is what created the living room 1 and 2 room names. It has to put them somewhere and probably just creates a new room when you disconnect by adding an incremental suffix to the room they were already in. Maybe I’m wrong though

I’m overjoyed this could be fixed now, but seriously shocked Sonos weren’t more transparent that they were working on a fix. They last told us specifically they couldn’t replicate the issue. Certainly a bitter taste in my mouth after this. Fingers crossed.

You’re correct, when bonding surrounds that have just been added to a system, they take on the room name with the incremental suffix. Which are revealed when the user unbonds them - I don’t see that as being the likely cause of an echo.

You can of course rename them now they are separate. In my own use-case I just change the suffix to ‘L’ and ‘R’ to identify which one is the left and right surround speaker.

Gonna focus on the positive myself but yeah, certainly room to be critical of Sonos’ handling