Yorick untargetable

I don't know if it's happened to anyone else but it happened twice in a row in a game i just played on the rift. Kindred would come top to gank Yorick, and have to use ult at which point Yorick would glow bright yellow kind of like a zhonya's and be untargetable, but still moving around. I know for sure the second time it happened Yorick's ult was active, and the first time I wasn't paying enough attention to tell you whether or not it was active. As far as I could tell, it was just when he was inside the Kindred ult, no matter his HP (meaning, he didn't go untargetable when he became invulnerable)