Spotify for android logs off automatically > offline music is gone

[Flox]

Spotify for Android keeps logging off automatically after some time (it's very different, sometime it lasts longer than the other).

The problem is when I log in again all my offline files aren't available anymore and I have to download them again.

Android however still says the size of Spotify is as big as it was with the downloaded offline songs.

I have 2 questions:

1. Why is Spotify logging off automatically?

2. Why doesn't Spotify see the already downloaded files after logging in again?

This happens even after reinstalling the phone.

Phone specs: Motorola X style