I have to download my playlist too often

[channell1313]

Every time there's an update, I have to change where my data is stored, tablet or SD card. My two playlist I had previously downloaded for offline and used for months, suddenly needs downloaded again. This wouldn't be a problem but I have satellite internet and only have so much download allowance. Why does this happen? I downloaded one playlist yesterday, almost 500 songs, today I have to download it again.