OK.  So here’s the deal.  I can update my music library but my SONOS ends the update with a message telling me that it cannot complete  the update.  It tells me to remove some music or playlists and try again.  In spite of that foreboding message, all of the “new” music is, in fact, added to my library and can be played . . . BUT . . . I believe that the system is truncating the library.  My music is organized in folders alphabetically and the last three folders (“X” , “Y” and “Z”) are no longer in the library.  I cannot recall the last time that I put a file in one of those last three folders.  So, it has not been obvious to me that this has been happening.  Now I realize that as I add more music to “higher level” folders, some is being eliminated at the end.  Apparently I have hit a “ceiling.”  

Is that what is really happening?  To test if I have hit the ceiling of a “library” capacity or just a “folder” capacity, I have split the files on the drive where they live so that the “U” through ”Z” files are in a separately listed folder in the library.  After re-indexing the library, the same problem persists.