SmartGroup requires objects to conform to rows, columns, contained blocks, or grids. If SmartGroup isn't working, it may be because objects overlap or don't fit into one of these four types.
Consider whether the overlap is necessary if it's due to overlapping objects. You can reduce overlap in the main structure by using "set absolute" or adjust object positions and sizes using "Resize & move, blueprint editing" to make items fit into rows, columns, contained blocks, or grids.
*Tip: Overlapping objects will flash orange so you can easily identify them for inspection.