Remove and re-add your music library pointer in the Sonos app? As a guess, right now there is something blocking the ability of the speakers to ‘see’ the location, hence no ability to re-scan it. 

If your library happens to be somewhere other than on your Mac, like an NAS of some type, it’s worth checking to see if there was an update to the NAS that turned off SMB v1. 

The music library is on the same Mac. How do I “Remove and re-add your music library pointer in the Sonos app”?

The same way you added it initially?

https://support.sonos.com/s/article/257

Thanks but when I go to the Manage tab . “ Music Library Settings” is greyed out also.

There was an S1 update I had to do in order to index my NAS from the phone (Android) app. Somewhere I read to let it update automatically, and that seems to have fixed the issue, but I'm afraid it'll auto update to S2. 

It’s i,possible to update to S2 automatically.  YOu need to manually download S2 in order to upgrade.