New IPad disrupts from 3G network regularily

My 2 new IPad regularily gets disconnected from 3G network when changing my geolocation. Only restarting the IPad's helps to reconnect. I already reset the network settings. Also the connection is lost, the 3G signal reception is shown very strong.

The problem seems to be very prevalent in Germany. I use different carriers ( O2 and T-Mobile).

Any idea?