Programmatically select group of shapes & connections

I have programatically selected a group of shapes and connections, but when I then attempt to use the mouse to manually drag the group around the diagram, only the shape I clicked on moves. I want the group to move as a whole as though I had used the lasso tool or multi-select. Code that selects the group of elements:

let selectionService = this.diagram.get("selection");;

What else do I need to add to get the desired behavior when dragging?

Could you share a screencast of what you’re doing? It just works for me: