Hi Tristan,
I recommend to pay attention that there are 3 levels of LiveControl objects - cue, master, zone, and also so called "surface" level, when you link the MIDI sliders to UI sliders. So, BEYOND offer multiple ways and it will give different results. In QS the MIDI were linked to Master Live Control object, directly and only to this object. It works always, and for all cases, master is master. In BEYOND you have much more detailed control what may be confused, but that is whuy we have QS where all is simpler, and BEYOND were number of options is definitelly higher.
What also recommend is makes a tests in clean setup. Create new MIDI profile, and work with it. Our APC profile is not that simple, and there may be conflicts between what you do and what already exists. Starting from a white page should be not bad idea.
If you like to control only Master L.C. object the on MIDI to PangoScript may be used code like this:
Master.Brightness=ExtValue(0,100)
One line only. PangoScript made for point to point connection, and this is one of examples.
Best Regards,
Alexey.