Evelynn ult cooldown not visible

I played an ARAM as Evelynn a couple of days ago, and at one point, I was frantically trying to use my ult since I was CCed and about to die. It went off at the last possible second, with the ult animation going off right as I died. (it was chaotic enough that I don't remember if the damage/shield of the ult went off, but I know the animation did) However, despite having used the ult, the cooldown didn't show on the HUD. Once I respawned, it appeared as though it was off cooldown, with no countdown visible, but I was unable to cast the ability. A couple of minutes later (I assume once it was actually off cooldown), I was able to use it again, and after doing so, the cooldown was visible. Only happened once, but it was a bit annoying having to guess for a little while when my ult would be up.