Milti-level .children filter

What’s wrong with this code?

 const a = $w("#toolbox").children;
 //main container Box children
 const b = a.filter(results => results.type === "$w.Box");
 //Groups composed of multiple Buttons inside main container
 const c = b.filter(result => result.hidden === false);
 //single visible Group based on Dropdown selection
 const d = c.children;
 //Buttons contained in single visible Group

a, b and c always return the appropriate values…
d on the other hand always returns undefined…
yet when I check $w(“#mygroup1”).children, it returns the appropriate values
furthermore when i check the $w("#mybutton1).parent, it also returns proper values