I have been a Sonos user for a very long time. 
The latest App and desktop (Mac) app updates have completed removed access to my local music files. I cannot re-add them and cannot find a solution. 
I am mystified why Sonos has done this and provided no way forward for us in this position. 
Given the many hundreds of pounds I have invested in my Sonos system over the years I am very upset and angered that this is the situation. 
Can’t add a single song anymore to my playlist. 
Atrocious!

if I was in America I think there would be a class action against Sonos to do something about this. 
 

to solve this in the short term allow us to re-install an older version of the app that will work as it did before these more recent updates.