[GAMEPLAY] Nautilus ult interation with kai'sa stealth bug

Nautilus ult casted did not go on CD. Ult indicator is on Kai'sa. Then the indicator disapeared without doing anything. Nautilus can cast his ult again, and it does what it is suppose to do this time.

I think it was caused by Nautilus ult casted right as kai'sa stealthed?? I am not sure.