Do you and your friend by chance reside in different countries. If so, that might be the reason why you see different music, since music can vary between countries depending on the permissions from rights holders.
We suggest that you go to your app's settings and scroll down and enable "Show unavailable songs in playlists" to see if the tracks appear. You can also reinstall the app for a fresh start. It might help here.
If you do reside in the same country, make sure you have Offline mode turned off, and that you don't use any VPN connection.