Thanks for your reply.
I will try to get your suggested logic analyzer, as it seems to be a realy good tool for our Arduino projects.

Nevertheless, currently the mysensors library seems to uses some Atmel328P commands, which are not 100% compatible with the LGT processor.

So I have to hope, that maybe someone can fix that on the library side...

Hi Rbonat,

thanks for your great help.
I finaly got it to work. After installing the boardmanager from "https://raw.githubusercontent.com/dbuezas/lgt8fx/master/package_lgt8fx_index.json", I got upload errors, due to the wrong upload speed (57600 instead if 115200 baud).

After changing the value in the board.txt file in the hardware folder I got it to work for my boards.

Again, many thanks!!