You may have read about this on the internet but here is a great article from iMore that explains what is going on .
No, Apple Music is not deleting tracks off your hard drive — unless you tell it to
ADELAIDE TECHGUY
TALK TECH WITH RICHARD PASCOE
Richard,Thanks for this. It may have answered my question. I subscribe to Apple Music and can not get all of my library music from my laptop (Windows) onto my iPhone 6. When I sync, nothing is transferred. I have music all the time through streaming, but only if I have phone reception (or home wifi). And in the country, that works just fine and dandy until I hit a black spot. I just want my music, on my phone that I can play – whether I am in Rhynie (home), or Black Springs or in the Simpson desert. Can you help me please. Happy to become a paying client. Regards, Matzy …
https://support.apple.com/en-au/HT204926
https://support.apple.com/en-au/HT204839