In my settings I had Only master on the bus ON... maybe that caused something ? I don't know...
This setting may cause the busfault, if there is more than one Profibus master.
The setting "only master" is only needed, if your want check for reachable Profibus slaves when there is no other master for example.
If there is a Profibus master on a running network, and you connect a PG with setting "only master" on, it starts to connect to the Profibus immediately with it's own timing settings, as it's thinking there is no other master which has to be respected.
Without this option set, the PG checks the bus level and telegrams, and only acts on the Profibus when it's allowed to do this.