computer vs mobile devices

[baaadoptions]

Hi all, I have a load of songs that play perfectly fine from both my library and my playlists on my computer but are "hidden" on my mobile devices.  I have tried synching many times but for some reason they will not download/play  to my iphone or ipod.  Why would this happen?

Thanks (very frustrated!)

[Peter__]

Hey! Welcome to the community 🙂 

Are those files which are hidden on your mobile devices local files on your computers spotify? 

If so, what format are the files in?

Peter