What is the year and model of your Mac?
Also, OS X version running? And version of Lightroom?
Astropad's shortcuts are preset for Photoshop. They can be edited for different programs in use.
How to do this -
On the Mac app, select Astropad's 'Preferences',
It will open a window with editable shortcuts for the sidebar.
Click "Set" then type the command on your Mac and it will register.
If there is a specific command that is not working, please let us know.