Link for the Log (too large for XDA) https://mega.nz/#!DxhhURCJ!ZGp4Lqm3elww9cW1YXnOzOzTPswBW7087x6UwqUMR1Q
Music app is official from Playstore. If I open your app it has remembered my changes, only if I kill the app with settings, I shows the defaults.
I pushed an update to the beta channel, please try it!
however, the issue here is that android N made accessing preferences a very difficult job, also, I suspect it has something to do with this issue, hopefully this update will fix it.