Good Internet/PC but Random Disconnects

Hi I have a technical issue while playing the game. Lately I've been experiencing random disconnects both in champ select and in game. During champ select,my client occasionally freezes at 0 second for couple minutes, sometimes leading to a dodge. During games I randomly dc for 5~10 seconds. In both cases, internet is working. Only the game is frozen. Any idea how to fix this? So far I tried using vpn, hextech repair tool, restarting my router, re-installing the game, suspending background apps. None seemed to work. I have a gigabit internet from Comcast (ethernet) and a nice build (Gtx 1070, i5-8400, 16g ddr4 ram, 250g ssd etc). Just to clarify this is not a fps/ping issue. It's just random disconnects though internet is working...

Thanks.