I would perhaps speak on the phone with Sonos Support about your trueplay issue, they may choose take you through several steps of changing the controller (if you have access to another) or perhaps a reboot/factory reset of your devices, one at a time, but I would see what they say first.
 

It would likely be worth you submitting a diagnostic report before and after trueplay tuning the room and post the references back here to refer to. 

Hi,

Thanks to you for your reply!

What is very strange is that I had managed to have the 2 surrounds at the same level and that above all I have made several TruePlay since then and that the 2 now sound at the same level. But since I removed them from my setup and re-associated them, it doesn't work anymore.

Yes, that would be nice of you!
I have already tried to factory reset the two surround speakers as well as the Sonos arc, but the problem persists.

I will try to do a diagnostic report first.

Thank you

I have just sent the diagnostic

For diagnostics without TruePlay: 2109223048
For dignostics with TruePlay: 1321187833

Thank you !

Can you perhaps contact/chat with Sonos Support via this LINK:

https://support.sonos.com/s/

Ok, I'll call tomorrow because today is closed.

You can also text/chat with support through the links on the support page too, if that assists.

Hello,

After contacting Sonos and sending all my reports, the person I got on the phone couldn't do much. I almost have the impression that they do not know their product on the support ... The person told me to use the balance to adjust my surround speakers, except that there is no balance on the app ... Same for the speaker distance, she didn't know it was greyed out after activating trueplay

What can I do ? I see that I am not the only one to have this problem on the internet to have the right speaker louder after TruePlay. I see that many people encounter this concern, and it is as if by chance always on the right one that the problem is found.

Ask the support to perhaps raise/escalate your matter to a Tier-2 engineer, to see if they can perhaps assist. 

Otherwise...

Only other options I can think of is to retune the speakers and in Step-1, alter your listening position to perhaps try to forcibly adjust the speaker-balance, or perhaps leave Trueplay switched off.

Unfortunately yes :/

And what I find weird is that before I reconfigured my Sonos system, it worked! By dint of doing several tests, after moving the Sones One SL during TruePlay, trying to put a plaid on the left edge so that TruePlay increases it and many other solutions while I activated TruePlay, it all ended up being work miraculously.

I realized that with all his solutions, he considerably increased the speaker on the left and that it was the one on the left which after these solutions sounded the loudest. So, I ended up reducing the thickness of what I was depositing on the left outline. I went from the blanket to the bed sheet, until I tried to do a normal TruePlay without resting anything on the left edge to increase it while I activate TruePlay. And miraculously, it worked! I was using TruePlay and the speakers were at the same volume. I had also made several in order to try to have the best possible rendering for my 3 speakers and each time, the 2 surround speakers were equal in terms of tone.

And then one day TruePlay crashed without me doing anything, moving or redoing TruePlay. Speakers on the right had resumed ringing louder without explanation. Also, just before that I had also noticed that when I turned the TruePlay button off and on again, the right speaker was louder again after reactivating! But when I did a TruePlay again, everything was fine. In short, already having a bug with the TruePlay activation button when I compared + the good speaker which had started to sound louder again whereas before it sounded correctly without me doing anything or moving the surround speakers , I thought it was a good idea to remove the surround speakers and put them back neatly into my Sonos ecosystem. But since then, no way to make the 2 One SL ring at the same volume! Very strange …

There is a question I ask myself. Does Sonos “study” how sound is played. And does it improve it on its own by playing the sound from the speakers? This could explain why, by dint of doing all these tests in my previous setup, I ended up getting the result I wanted ...

I think I just found the problem!

It seems that switching from "ambiance" to "full" reading to "music reading" solves the problem! Strangely, once "full" mode is activated and after having a TruePlay, the two surround speakers are at equal volume. Also, I also noticed that turning "full" to "ambience" during playback again makes the surround right speaker sound louder. And once back to "full", everything is back to normal and the 2 surround speakers sound at the same level again.

The same goes for activating and deactivating TruePlay. Once TruePlay is turned off and back on again, the speaker on the right is louder again. But once gone from "Complete" to "Ambiance" then from "Ambiance" to "Complete" the 2 surround speakers are again at the same level .. Very strange !!

PS: I want to point out that the sound bar and surround speakers are mainly used for television. And this is all really about the use of television.

That is indeed odd. That setting should only be affecting playback of music, and not on the TV’s digital input. Might be worth posting an ‘after’ diagnostic for them to compare, to see if someone could forward the data to the engineering team. 

Indeed, I find it weird too but it seems that it works!

Then I will be curious that other users try to do the same operations to compare. In other words, select “full” instead of “ambience” in music playback, then do a TruePlay to see if things are better afterwards or not.

Anyway, regarding my comment just above, I understand better why I suddenly realized everything sounded better the first time around. I had already selected this option before and hadn't realized that this was what had solved things. But indeed, this bug is very strange ...

I have the exact same problem since day one.

Arc+ 2 sonos play one.

After trueplay calibration equalisation is better, but le right surround speaker is Always louder.

I asked Many Times during beta software the possibilitie to set right and left surround levels separatly....

Hi,

Did you however try the method I described above? That is to say to put "full" in music playback "and to perform a TruePlay again and then to compare?

Hi.

Yes i did, it didn't solve the problem.

I think it would be cool to add this feature, for example be able to set right surround speaker to -5 and left surround speaker to 0.

Because all people doesn't have a dedicated Room for home cinéma and multiple configurations....

Effectively ! I agree with you.