Login failed after firmware upgrade from 20.49 to 21.20.6

The story: I use the WiFi capabitily of the powerwall2 to get PV data for my weatherstaion. With FW version 20.49.0 login was required. With the help of jrester’s python api I got the data again. But with FW 21.20.x login did not work any more. Calling Tesla support was helpful and quick: they downgraded me back to 20.49 the same day.
BUT: last week I had 21.20.6 again.
SOLUTION: adressing the powerwall2 with it’s local IP-ADDRESS. Before I used the local NAME. Which is rather strange, as pings to the name are properly resolved.