On the group property editor tick “collapse group when hidden” (it’s something along those lines) + then also tick “animate the collapse”. Should do exactly what you need
Perhaps the issue is the amount of spacing you have between A-B and B-C.
What I would recommend trying is having Group B contained inside another Group, which is visible on page load. But the actual contents of Group B are not visible unless your condition is met. (This new group would contain a bit of buffer space between A-B and B-C).
The other option is to make use of the Drag/Drop features. (Ie. when x condition is met, move to y location on the page, by specifying the location of another option (Group A).