I could not make the DA of "Selection Change [Interactive Grid]" to fire upon page opening/loading. It fires when I move to different records in the interactive grid after the APEX page initial loading. However, above issue could be resolved by turning on the “Lazy Loading” option on the interactive grid region (The interactive grid is based on a table with less than 100 records in my testing, so there is no performance issue here). I wonder if this behavior is constructed by design: the DA of "Selection Change [Interactive Grid]" is designed NOT to be fired, unless the “Lazy Loading” option on the interactive grid is turned on? Thanks for any inside info!