Game feels extremely unresponsive

Since the new patch I've been noticing serious input lag. Some abilities are being delayed several seconds in activation, but I have no lag elsewhere in the game. Movement feels fine, items are purchased find, etc., and my ping continues to display around 47-48 ms.

For example, in a recent game. I'm trying to defend the Nexus against a Fiora, Viktor and Vel'Koz as Malzahar. They start attacking me, no CC has gone out yet and I'm spamming my Q, W and E keys. It takes them a good 2-3 seconds to kill me, during which time I managed to use ZERO abilities despite spamming my abilities the entire time.

It's happening on auto attacks, too. I've lost count of the number of times I've missed CS because the auto attack was greatly delayed in starting.

Everything feels slow and unresponsive. The game is borderline unplayable.