PC cannot connect via UDP to Companion

I’m using MAVSDK on my PC, which is connected by usb-c to a siyi HM30 reciever which is bound to an airunit on the drone.
The airunit is connected to a Pixhawk 6C flight controller, which in turn is serially connected to the companion computer (raspberry pi 4).

The problem that I can’t understand is that whenever my PC is connected by Type C to the reciever, everything works fine; I can establish connection with the companion computer.

But when my PC is connected to the reciever using the UDP cable, I cannot establish connection with the companion computer anymore.
I have confirmed that in both method, the MAVSDK does detect the flight controller.

Do I need to connect the Companion computer to Pixhawk 6c through ethernet, instead of serial? Since my flight controller doesn’t have an ethernet port, I have been unable to try that.
Has anyone else tried something similiar or know a suitable solution?

I appreciate any help or suggestions,