iPhone4 Libratone app screen goes black

Hi There

I am trying to set up a Libratone Zipp with my old iPhone4 running iOS 7.2. It connects ok both over Wifi and Bluetooth, but when I try to use the "Libratone" app (I think 4.1 - downloaded a few days ago) to change the radio stations the app screen goes black.

When restarting sometimes the app comes back, but occasionally I need to hard restart the phone.

Has anyone experience with this combination of old iPhone and (newish) Libratone Zipp speaker?

Many thanks for any help!

Sarei