This is so frustrating... it is happening to me at least once a game sometimes twice. I look at my ping and fps and neither are spiking, I just lose control of my champion for about 5-6 seconds and no input commands work. In my last game I watched 3 of my own minions die while I stood under the enemy tower. I started taking turret shots, watched my adc start question mark pinging me, and then watched as thresh hooked me. I could not move at all but I could see everything that was happening in game. This is now almost an every game occurrence for about 5 seconds at what seems like a random time in lane.
I dont have to reboot or get locked out of the game... the game allows me to move after about 5 seconds. I have been playing on the same connection for years without any issues and with a rock steady ping at 63 ms.