Is Nocturne's ult bugged?

I am having a lot of trouble reactivating Nocturne's ultimate for some reason. I'll be spam clicking the recast on an enemy and it simply will not initiate the dive effect. I noticed that when hovering over his recast, the tooltip text is replaced with a constant id, something like nocturne_ultimate_tooltip. I've reinstalled league of legends and my keyboard drivers yet the issue persists. Is it just me or did something happen recently to break Nocturne's ultimate?