Heltec LoRa 32(V2) Example LoraWan not working

[dm6tt]

Hi guys,
I'm trying to test the example 'LoraWan' provided with this packages.
It works fine with an V3 board, data are received by TTN.

When I switch the board to the V2 version (and change the board type in the Arduino GUI) the code compiles and get flashed, but no data are reveived at TTN.
In the console one can see that it tries to join.

Is this libraray not compatible with the V2 board?
Any hints how to use it with the V2 board?

Thanks
Marcus