Your speakers are all running 11.2, your controller is 11.1. That mismatch would likely cause this issue.

And no, I don’t know where you can get the 11.2 controller. The current version is 12.0.2, at least for an S2 system. 

11.2 is the current S1 controller. You can update to 11.2 from within the app itself :

   Sonos S1 Controller > Check for Updates...

Many thanks:  it works now.

The real irony here is that the “Update music library” option truly doesn’t care what version anything is. It is a single UPnP call, that just goes to the AssociatedZP. There is no version dependency whatsoever. This API has existed since the very beginning of Sonos, and has never changed.

There is no technical reason for this menu item to ever be disabled. And yet it is. Its as if Sonos engineering wants to generate support calls and confused customers. Bizarre.