Lagging around 6-10 min

I have this problem for a long time (like 4 patches). My fps drops from 100 to 40 without reason. When I was looking for help I noticed 5 months old post on board with the same topic. ( https://boards.na.leagueoflegends.com/en/c/gameplay-balance/0Tb8Idtd-every-game-lags-at-6-min-or-10-min ). New comments have been posted there with the same problem and it seems like riot doesn't care. Any help or solution?