App is incredibly slow on iPhone 4 iOS7

[kunstlump]

After reinstalling the app several times it's still incredibly slow on my iPhone 4. the bootprocess, searching, selecting songs etc. everything takes several seconds. opening the app and playing the last played song takes up to 1 and half minutes! reinstalling makes no difference and I'm using the app only inmy private WLAN network which can not bethe reason.

[kunstlump]

...to change the artist and start shuffle playing took 55 sec. that's unbelievable! anyone an idea?