Q: iPhone SE and Radio Streaming Apps: Audio in Background Arbitrarily Stops

New iPhone SE (16GB): I use two radio streaming apps:

https://itunes.apple.com/de/app/das-dradio/id439874065?mt=8

and

https://itunes.apple.com/de/app/fip/id310237906?mt=8

On the iPhone 4S, that I had before, I had some problems with the first app, none with the second.
Since I have the iPhone SE the streams from both apps constantly stop.
Sometimes it is enough to tap stop/play (the apps seemingly think they are still playing), sometimes I have to throw the app from the pitcher and start it again.

I don’t get more than a few minutes of streaming from both.

I have no problem playing music from the iPhone in the background. Video streaming works fine, but that isn’t in the background obviously.

Audio streaming on my MacBook and iPad 3 work fine (same apps with same versions on the iPad 3 by the way), so it isn’t my DSL connection.

Any ideas anyone?