Weird Lag spike 10-15 minutes into game.

When im playing league, i get a weird lag spike between 10-15 minutes in game. If i leave the game and rejoin it gone for the rest of the game. This lag spike doesnt make my Ping go up at all. It's always at 60-70 ping. But this lag spike makes everything have a 10-20 sec delay every time. I dont know why this is happening. It's not my PC, i checked, it's not my internet, also checked and this only happens on league. i tried to uninstall and reinstall the game but it still happens. Can someone help me out? ( I already made a ticket 2 days ago but still nothing from them yet)