The engine is defective after 2700 km. There is a very loud whirring sound. The performance is almost completely gone.
OP in comments (translated):
Edit: The whole rear wheel including sprocket and the controller were sent to me, I changed both and everything works fine. Very nice service from NCM. It all took a total of 2 weeks because I first suspected the engine and swapped it, but the whirring was still there. My specialist workshop then diagnosed that it could only be the controller. DH: If the new motor receives wrong control signals from the controller, every new motor sounds so gruesome. Controller replaced with a new one and everything is fine.
The motor and controller were sent to me under guarantee. now things are like at the beginning. optimal solution of ncm.