[GAMEPLAY] Elder drake becomes untargetable

I just played a game as Jhin and lost the last hit on Elder Drake because something made it go untargetable for my abilities and autoattacks for about 4 seconds. I just walked into the pit instead of attacking this huge dragon - which to be honest you cannot miss clicking several times.

Usefull information : I think I got whimys and a Lulu Shield on me, and this happened after the drake took a few hits from corkis Ultimate.