Hi,
the latest SC version (9.3.008) seem to have fixed the issue with Select2 elements in forms open as modal, but modal forms are still not rendering all elements correctly.
in come cases, grids apps linked as details in master forms apps are not shown at all when the master form is open as modal (and work perfectly when the same form is open not as modal)
A manual or programmatically-triggered reload of the form frame, fix the issue: the detail grid is then visible.
Note: this is an old bug, not inroduced with the latest updates