Spotify crash - iphone 6 - online

[Johnhawk]

Hi,
I'm experiencing a lot of spotify crashes : the app just shuts down and brings me back to the main screen of my iphone.
I've noticed that the issue happens ONLY when I'm connected to 3G/4G or wifi. The apps remains stable when I'm on the plane mode for instance.
I have roughly 20 gb of songs that i try to synchronize to listen offline.
A corrolated issue is that i see the downloading bar on the top, it starts downloading songs then stops way before reaching the total number of songs, leaving me with unsynchronized songs.
I've tried to re install the app and format my iphone but the issue remains ...
Could someone help me please ?

Thank you very much