Randomly my r just wont cast

So just happened to me playing Qiyana where i was spamming r and it just wouldn't cast, when i held r it show'd the trajectory of the skillshot but wouldn't cast, after dying because of this i sat in fountain for a whole 20 seconds spamming it and still wouldn't cast, i had to unbind and rebind it for it to work again. It had been working 3 minutes earlier and i hadn't made any changes since i last cast it.