Hello @monkescripts I have the same issue. I am also using the tag v1.14.3 from PX4 Autopilot and the branch release/1.14 from px4_msgs. Are you using that branch too?
I am using the Isaac ROS packages, which involves using dockers where ROS2 Humble is running inside. I am able to connect through DDS, but I cannot see the topics. I assured the B/s in Mavlink console, same as you.
Btw I am cloning the repository with this command:
git clone https://github.com/PX4/px4_msgs.git -b release/1.14