I suspect that the Raspberry Pi isn’t setup for this ‘auto’ connection. I’ll look at the instructions and maybe setup the RPi as a bring. I have the stuff, just have’t done it.
I think you are right in that even with RDS, MAVPilot needs that first UDP packet from the Pi to know what address to send it to. And that’s the bit that is broken.
I’ll try and find some time to get a fix, but you have a solution for now, so at least you are not blocked