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I was playing Riven in my last game and after one time I used my Ultimate but never used the slash, and as it ran out all of my other abilities turned Grey and became unusable, I also was unable to use my Ghostblade and my Recall, Flash was greyed out as well but ignite was not for some reason( though I never tried casting it). I alt-F4'd and reconnected and the bug was still going on, however once I died it went away and I was able to play the game as normal.
I wish I had more information on what I was doing when it happened but I wasn't really paying attention, I think I was using Q to run away as my ult timed off.
Edit: Guess it's already known, took this from another thread:
"[GAME BREAKING]• If Riven is knocked back while she is mid-air during the third hop of her Q, she will have all of her abilities permanently disabled, including summoner spells and recall"