It may be the editing, which isn’t perfect in the first half, but adequate. In the second half, elapsed time isn’t clearly defined, and some character introductions/relationships/reintroductions are a little clunky as a result. Chemistry between Patel and Rooney Mara is average. The scenes they share extensively together (not a ton) is when Lion becomes a tad clichéd and its pace compromised
But even with that, Lion does a lot more to be legitimately emotional than the average solely Oscar-centric movie. In simplicity, a moving tale is found.