Apple Music turning all my songs to stream?

Hi all- I've got an external library on Mac with over 100k+ songs (mp3's) and recently found some "!" next to some tracks (which I've now recovered) but tonight when I've clicked on various tracks, it's automatically turning stored tracks into streams? Any idea on how to stop this happening? I thought my library was fine until a few days ago - restarted Mac, opened Music to find this and now freaking out. Gotta say, this is now ******* me off as recently re-built old library and now this is happening.

Any one else had this problem or any ideas on what to do? (apart from moving library :-(