Music files in external SD card doesn't reflects on Google Play Music in Galaxy S7 Edge?

Samsung is aware of this symptom which may appear on some devices and this is issue of Google Play Music itself. This is already known issue on internet. Regarding this, Google will release improved Play Music to resolve these symptoms and at that time new update will be released to enhanced version in Play Store.

Before the time, we recommend to use after clearing application data and cache of Google Play Music by following next steps Settings > Applications > Application manager > Play Music > Storage > Clear data/cache.