Flash not working at all

Just played an ARAM as and was on my F key. I could not flash at all. I tried setting it to normal cast and hitting F displayed the circle but I couldn't click to flash. I even tried it on the platform. It didn't matter if I was stealthed or not. My D (clarity) worked just fine. Very strange bug I have never had this issue before. I downloaded the replay but can't find it. =\