@FMA,
Not sure if this helps or not, but I once came across this issue, albeit with different Sonos products - and it was quite a long time ago. I resolved it by first unpairing the speakers and ‘factory-resetting’ one speaker, then I added it back to the system… before I then ‘factory-reset’ the second speaker and also added that back to the system.
I stereo paired them again and the issue was resolved. However, I’m not completely sure, but I may have also renamed and swapped the two speakers around afterwards too, so that the left speaker became the right one etc.
Note however, if you do rename your speakers and currently use them as accessories in the Apple Home(Kit) App, you should ideally remove, or at the very least, rename the speakers in that App aswell.
Anyhow, the reset steps helped to sort my issue and I have not seen it again since.
So maybe speak to Sonos Support first and perhaps consider trying the above suggestion, if all else fails. HTH.
Unlikely that there’s anyone in the community that can answer your question, probably better if you were to call Sonos Support directly to discuss it. They could likely look at your diagnostic, and suggest whether it’s peculiar to your setup, a hardware issue, or a software issue.