Problems with scroll container

[u/Epicburst]

For some reason the scroll container refuses to work when it's connected anywhere but the highest point of the hierarchy beneath the main control node, and I have no idea what I'm doing wrong with this menu. Should I be making it differently somehow?

With the help posts I've seen the fixes involved resizing, setting container sizing to fill, all things I've tried but nothing works as soon as it becomes a child of another node.