I suspect it was talking about 

although there has been no discussion about dropping support for local files, just a restriction on the search function. 

Thanks, appreciate the clarification.  

Another poster received a similar message, they don’t mention search, they say music library. This link should go to their comment 
 

Also see Further sidelining of NAS Music Library in new Sonos App?? | Sonos Community

I think the comments above referencing 

are probably what you need to look at, rather than the post you’ve marked as the answer.

Sonos devices will no longer be able to access music libraries via the SMB1 protocol or HTTP so if you are using a really old NAS that only offers SMB1 you will lose access to your music. This is not a good thing for those of us with old storage drives as it’s quite unlikely there will be any capabilities on them that will work instead.

For me the solution was to buy a new NAS that has SMB2 support - that would be pretty much any new device on the market (I bought QNAP but people like Synology as well). One handy side-effect is my QNAP NAS also supports Plex and that is a much more flexible way to access my music anyway!

Thread specifically on feedback for the new Web App …

Cette nouvelle application avec soit disant de grandes innovations est totalement inexploitable avec des bugs et des régressions indignent d’une pareille marque. A ne surtout pas installer, le retour en arrière avec IOS est impossible. 

Que les informaticiens travaillant pour Sonos retournent à leur clavier, la pente va être dure à remonter. Pour info, avec cette application, impossible de répartir différentes sources sur  différentes enceintes. C’était la force de Sonos; à ne surtout pas installer, aux risques que votre système ne soit inexploitable. Inimaginable qu’une application aussi buggée ait été déployée

So my Sonos automatically removed my music library as I feared.  I checked my NAS server and it was set to SMB and not SMB2.  Updated it to SMB2 and then tried several times to add the NAS server back using the URL.  The behavior was the same each time.

• Chose the option for a NAS Server and added the URL
• Sonos then found the library, said it would add the files
• The Settings window showed the spinning prompt for some time
• The Settings window crashed at one point and then reloaded
• The Settings window again showed the spinning prompt for some time
• Eventually a message came up saying that the music share “is no longer available”

Just to be clear, Sonos did not erase your library, it does not have privileges to delete files. You certainly may have lost access to them from your Sonos, due to the removal of SMB v1, but the files should still exist on your NAS. 
 

Based on your post, it doesn’t sound like your update to SMB v2 didn’t ‘take’, you may want to contact the Customer Service folks at the manufacturer of your NAS. 

I can see on my windows PC that it is connecting to the NAS Server using SMB 2.  So there should be no reason for the Sonos App to work.  No legitimate reason, anyway.  I have been using this NAS for years.