GPS + Rangefinder = Confusion

I am building an autonomous boat using a Pixhawk 4 flashed with ArduPilot, a Holybro F9P GPS unit, a Blue Robotics Ping sonar, and a 1000 mW Dragon Link receiver.

Initially I integrated the Holybro F9P GPS, a Holybro Pixhawk 4 GPS unit that came with the Pixhawk 4, and the Blue Robotics Ping. The Holybro F9P GPS was plugged into Serial 4, the Pixhawk 4 GPS into Serial 3, and the Blue Robotics Ping into Serial 2. I connected to the flight controller via USB, not by RF link. With this setup, the Pixhawk would not recognize one of the GPSs whenever the Ping was plugged in. This was solved somewhat by not using the Pixhawk 4 GPS unit and only using the F9P.

Sense then, I integrated a Dragon Link Telemetry system. Currently, the Holybro F9P is plugged into Serial 4, the Blue Robotics Ping into Serial 2, and the Dragon Link Receiver into Serial 1. Now, the Ping will not work at all (sonarrange and rangefinder1 both read 0). The ping works when pugged into a PC with a usb to uart adapter however. Also, when the ping is plugged in, the Pixhawk 4 will not recognize the GPS.

I have religiously followed the procedures below and updated the Pixhawk’s Firmware multiple times. Attached are all my parameters. Any suggestions on why the GPS wont work when the Ping is plugged in and why the Ping stopped working after integrating the Dragon Link Receiver? Thank you!

2021.07.09_with_ping_on_startup.param (16.2 KB)