Hi. The smite heal proc ability doesnt work on the lagon fight. I assume this is because he is so large the smite hits off screen somewhere in the center of his giant hit box. If you make his hit box an oval or a rectangle with the center closer to the player it should fix the problem i think.
This is a known issue with Lagon, due to his model size where he gets hit is too far from the ledge foe the player to be in Smite’s heal. Lagon’s hitbox is actually not the issue since it extends all along the edge of the ledge so you can hit him wherever you are (as long as you’re close enough to the edge).