Offline Music Bug

[Nayibmc]

I always have all my music available offline (by pressing the very vulnerable Available Offline button). It works fine. But today I took out my phone's (Z5) old SIM card and changed it for a new one. When the phone was on again, I opened Spotify and I had to log in, something that shouldn't happen. I noticed that my SD's storage was the same, so the offline music shouldn't have been affected, and maybe it wasn't, but I couldn't listen to it offline and couldn't activate the Available Offline option.
I "fixed" it by going to the settings and changing the storage from internal to SD (even though it should have been set to SD) and now I'll have to download again more than 2400 songs using 2Mb connection.
Why did that happen? And how can I prevent that from happening again?

[Yrrah1]

Perhaps when you took out the SIM the Z5's SIM & SD storage settings were affected (reverted to factory default etc.?)

[Nayibmc]

Maybe. Anyways, I'm getting used to downloading those 31GB at least once a month -_-