I’m having the same issues many have reported to access my iTunes library, I can get it to recognise the library and play my tunes but as soon as the computer storing the files goes into standby the tracks still show but won’t play saying they have either been moved or the computer is off, even if I wake up the computer they still can’t be found, if I restart my computer the files are there and will play again this is on an IMac 

I used to use a Mac mini but the music library will not show up on this one no matter what I do and I have tried all the options to make it work

this is really spoiling my experience with Sonos and I’m too far into the brands products to go to another system