Honestly I would probably filter UDP over udp.port==6000 as while 6000 is supposed to be the correct client port to broadcast from the apm.sh says the server/Pi is running on 6001 so from a client side capture if all I saw were outgoing requests from the client and no response from the server it only accounts for one side of the traffic. I'd likely need to run tcpdump against wlan0 with the udp switch/filter (or no filter) to capture the server side and what it is doing. I have no problem doing all of this it's just an epic pain in the ass if there is a ROS or other log I can review.
Edit: Capture at the link below, there is nothing going out on port 6000 and the only UDP traffic is DNS broadcasting from other apps on my Mac. I captured my SSH in it as well to show it's establishing a connection correctly. I have no firewall enabled on the Mac either so why APM Planner is not sending out doesn't make any sense. Maybe I should try other programs like Mission Planner or QGroundControl.
Don't really see any benefit to running tcpdump on the Pi at this point if APM Planner isn't sending anything out.