I was in contact with the service staff but they could not help me. Last proposal was to try another platform than traccar.
This is not helpful.
Furthermore, my device has some other problems like: sporadical no IP assignment via DHCP, sporadical loss of wifi connection, sporadical no internet when connected to a VPN as client and so on.
From hardware point of view, this device seems to be great but the software is a disaster. I am looking in parallel for alternative device because this one cost me so much time until now.