A parent item that doesn't draw (i.e. an Item or a Rectangle with color: "transparent") and has clip set to true will not cause child items to redraw when its height/width changes to "reveal" them.

I've attached a basic example to demonstrate this. Running this file using 5.2.0, clicking the button will animate revealing the full square. In 5.2.1 and the 5.3 beta, clicking the button appears to have no effect, despite the Item's height