I have the same issue. I have the iPhone 7, and if I play apple music the song title and artist will come up, but if I play from Spotify, it rarely displays the song info.
[SOLVED] The issue is your AVRCP version. Most likely you will need to downgrade it. First, you'll need developer options enabled on your Android (Settings>About Phone> then tap Build Number 7 times). After developer options are enabled, go to Settings>System>Developer Options>Bluetooth AVRCP Version. Try changing AVRCP version, restart the phone, and see if this fixes your problem. AVRCP is what controls the metadata that is sent to your bluetooth device.