[Gameplay] Ultimate (R) stops working.

I've had multiple occurrences of this bug in this last patch, in both Howling Abyss (ARAM) and Summoner's Rift. I currently run no third-party programs/overlays.

There's not much to describe other than your ultimate failing to cast randomly. So far I've had this bug happen with multiple champions, three of which - Ahri, Akali and Diana - share a similarity: they all allow multiple casts of their Ultimate (Diana being the only one who has a condition for this to happen). In these champions, sometimes the first cast works and the following ones don't, or sometimes not even the first one will work. I've had this bug happen with Veigar, Ekko, Cassiopeia and Brand as well, all champions which only allow one cast of the ultimate.

When the bugs happens - and it happens multiple times per game, you can still type normally in chat (R key works normally), pinging your ultimate will show the "Ultimate - Ready" message, all other abilities work, warning pings work, everything works normally. Clicking on the Ultimate icon to cast it also doesn't work, meaning the bug isn't tied to keyboard problems.

This bug is completely random - sometimes the ult will fire, sometimes it won't. I do not know any specific steps to reproduce it other than playing these champions (didn't encounter the problem in pratice mode), and video proof is worthless unless it is from a player POV (which I currently do not have - I'll be setting up Plays.tv and i'll post a link here if it does happen again), because it's undetectable in Spectator mode. It's also pretty hard to take a screenshot of something that is not happening while you're in a chaotic fight that you end up losing because of this.