"no selections are available" redux

I have been running this Sonos setup for years and it’s been fine. This is a relatively new problem.

Symptom: when I browse through the Sonos UI into “Music Library” and try to see items in any category (Artists, Albums, Genres...) I get “No selections are available.” I have had this problem before. Last time it went away by itself after an hour or so. This time it has persisted for some hours. Original post here.

I am able to play Spotify, so the Sonos system is connected and working--at least mostly.

The next logical supposition would be that something is wrong with the NAS device where my music files reside. No sign of a problem there, however. I ran diagnostics on the Synology hard drives just yesterday, and they are fine. Furthermore, from my Windows 11 desktop I can browse to the same NAS fileshare that Sonos is configured to use, and all the files are there, visible on the network. And I have not touched the permission settings on that Synology fileshare for a long time.

More details:

I see the same symptoms from the Sonos iOS app and from the Sonos Windows desktop app.

I have checked for updates. My apps are current.

I tried powering the Sonos Connect off and on. No effect.

My music library has about 15,900 files, so this doesn’t look like a capacity problem.

Associated Product
---------------------------------
Connect: 
Sonos OS: S2
Version: 15.11 (build 76247270)
Hardware Version: 1.22.1.4-1.1
Series ID: D100
WM: 1
---------------------------------
Play:1: 
Sonos OS: S2
Version: 15.11 (build 76247270)
Hardware Version: 1.20.1.6-1.2
Series ID: A200
WM: 1
---------------------------------
Play:1: 
Sonos OS: S2
Version: 15.11 (build 76247270)
Hardware Version: 1.20.1.6-1.2
Series ID: A200
WM: 1