Syndra's ult timer

This bug happens multiple times in one game. Most times after you ult as Syndra, the ult goes on cd, and the numbers pop up in the box, but the box doesn't start filling in gray. It may be caused by dying while ulting, but after the first time, you don't have to die for this bug to occur

Edit: This bug always occurs the first time you ult, and it no longer bugs out once the ult reaches level three