Keyless engine start/stop malfunction.

Moin Moin, has had a Phaeton GP2 in my possession for two days. My problem: I open the car without a key and start the engine without a key.. after a 10 min drive I can no longer get the car out. Then I have to put the key in the ignition lock and manually stop the engine. Then I can no longer get it without a key. After a break of about 30 min. I can start the car again without a key and even stop if it didn’t run too long. Someone has an idea?