FLAC -> Apple Lossless won't play on Sonos

[tcp1p]

I use iTunes to manage my music library which is stored on a NAS and I also have a Sonos system which uses/plays from my music library on the NAS.

As iTunes doesn't support FLAC, I simply convert my FLAC files to Apple lossless (ALAC / .M4A) then import them into iTunes.   However, I've just found that the Sonos system is not playing the more recently converted ALAC files,  Sonos gives an error 'unable to play [filename] - the file is in an unsupported format.'  The files do play on iTunes and on Windows 10 Groove player.  If I use an alternate converter, e.g. dBpoweramp it works on iTunes, Groove and Sonos!

This may be unrelated, but I also note that the metadata is being manipulated, and when iTunes imports it after it has been converted by Switch, iTunes gives it a different name to that it previously had and also to what the dBpoweramp converted file is renamed to - iTunes renames it based upon the metadata to and gives it a filename of 1-01 xxxxx.m4a, 1-02 xxxxx.m4a or similar, whereas normally it would be 01 xxxxx.m4a

Any ideas?

[tcp1p]

Fixed:    The Apple Lossless Output Options need the following settings to be changed from the defaults

  Sample Rate: 44100 Hz

  Channels: Stereo