But maybe it is because there’s another top grab area inside the courtyard ?
(not explained in documentation, there is no “Grab Area” subsection in “Package” section)
Is it normal that grab areas only work if “Top Grab Areas” is set to visible ?
No, that’s intended because you want to disable top grab areas when working on the bottom side, and vice versa. Same for the “Reference” layers which also enable/disable grabbing packages by their origin cross.
Every polygon has a “Grab Area” property to easily use them as grab area too.