@Joseph-TP Since I have connected the Raspberry directly into the BE550 it's working now. Maybe this should be made clear on the UI when setting up an isolated device. Thanks everyone for helping.

@woozle Thanks for testing this, I do indeed have a 24 Port switch connected to my BE550 and the Raspberry is plugged in there. Does this make a difference?

I have a piaware ADSB service running on a raspberry PI. The device is connected via cable to the router. I want this device to be isolated. I used the device isolation feature in the securuty...