Random, very unusual input lag without ping spikes or FPS drop

Server: EUW Details: Sometimes when playing a game, my character doesn't respond to commands I issue. It appears up to ~ 10 times in a game that my character just stands still for about 2-5 seconds and doesn't respond to any mouse click or ability button I press. The thing is: I can see that the game actually registers my mouse clicks, because the blue arrows when doing a right click appear on the ground. Also, everything else doesn't have that kind of lag. I can see every other player's actions perfectly and fluently, which is super annoying because in lane, this lag can easily cause a death. My ping is consistantly around 30 and my FPS never drop below 60. This problem appeared yesterday and I've experienced it in every single game after. I already did a complete client repair and it changed nothing. Then I reinstalled the game and again, nothing changed. Several router resets later - the problem persists. But only in League.
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