Boucing projectile spells are usually able to bounce off of invulnerable or hidden units. This is to prevent them from completely fizzleing only because one target turned invulnerable/hidden before projectile impact.

As a comparison, other bouncing projectiles can bounce off of invulnerable and hidden units: Paralyzing Cask, Mystic Snake and Chain Frost.

Repro:
1. Pick Bounty Hunter and level up Shuriken Toss and Track
2. Create an enemy Outworld Devourer and Bane
3. Cast Track on any of them
4. Cas Shuriken on the same enemy
5. Have the enemy cast Astral Imprisonment/Nightmare on self before the projectile reaches them

Result: The projectile does not bounce off of the now hidden or invulnerable enemy. It completely disappears.

Expected: The projectile should bounce off of them, without harming it in any way (no damage, no stun). Being hidden or invulnerable should not stop the shuriken from bouncing to other nearby valid targets.