If you are taking look into volume control there is also a problem with picking up the phone during playback. When you hang up, Xeno volume (the one with Miracast icon) goes all the way up. I have lineage 14.1.
Some time ago I posted this problem. I think I have found a cause. I'm using TTY vco as I have earphones without microphone so I can have my earbuds in ears while speaking through phone's mic (it is the phone app's accessibility option). It's the same with lineage 15.1. I don't know if it is Android wide or lineage specific. There is also a question how it works with complete hands free sets (Bluetooth or wired without tty vco)
To reproduce the problem:
1. Set tty vco in phone accessibility settings
2. Attach headphones without mic
3. Start playback in Xeno
4. Answer the phone call
5. Hang up (ATTENTION! Now music volume will go to the top)