Spotify on iPhone never goes online on mobile network

[chilledbits]

I really hope someone has a solution for that one: 

I use Spotify heavily on my iPhone.

Unfortunately even though the switch "Offline" is off and even though I am having full connectivity with LTE. I always have the annoying message: Spotify is offline.

I am not logging in via Facebook, just usual credentials. 

I logged out and in again.

I quit the app, restarted the iPhone.

I also reinstalled Spotify.

What can I do? This is super annoyng. 😞