Followup:
During tests I found, I cannot login to the comman line interface. Trying to log in I get a browser message:
Secure connection Failed
An error occurred during a connection to localhost:8885. Peer reports it experienced an internal error. Error code: SSL_ERROR_INTERNAL_ERROR_ALERT.
On the command line I get some errors too:
application_uid=ttn-loranode01 error=error:unknown:unknown (transport: cannot send secure credentials on an insecure connection) namespace=applicationserver
So it seems, there is some thing wrong with the ssl/tls-setup, but no idea, what.