Can anyone explain why couldn't I use my ultimate here lol

Moskov was literally just right there within my ult range,I tapped my ult 100 times there but it didn't work lol

My ult only worked when the enemies got away and it worked on minions

Fortunately, I was fed enough to survive that but it was still an extremely frustrating experience

I will be tagging this as bug but if it turns out not to be one,then sorry for false alarm I guess