Package not visible after sourcing local_setup.bash, but works with setup.bash

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If I run

source devel/setup.bash

I can run rosmsg list and see all my messages and autocompletion works for my nodes. But if I run

source /opt/ros/melodic/setup.bash
source devel/local_setup.bash

It should be the same, right? Even the CMAKE_PREFIX_PATH var is identical after each. Yet in the latter case, I can't see any of my messages with rosmsg list

ROS project is a fork of AirSim

The CMakeLists.txt of the primary package is here