Is this a bug?

So there we three squads left and I was a solo because my teammate died, i'm playing mirage and I had my ult and I was waiting for one of the other two squads to take the other out so I would have a chance. when the circle was shrinking I was about to use my ult and I couldn't use it because it suddenly said it wasn't charged and went down to like 96 percent was there a reason for this cause I got so close to a cheeky win.