Some games, I lag for no reason

While searching for a cause, i bonked into that topic : https://forums.na.leagueoflegends.com/board/showthread.php?t=4009879

So the issue must be quite old, i've never heard of it before today, but this week this happened to me twice

Both of these games I had a stable 400ms ping for no reason, and right after the game i drop back to 30ms I s there any way to know why and how to fix hit ?

This might not seem much of an issue, but this is obviously infuriating to lose one game for free and to have all your team blame you for it I didn't ask for anything and i can't just hold the other cheek while everyone is spitting on me, so I get toxic, and everybody else does, and this might cause some unnecessary bans

So yeah.. This is pretty crappy, at least way more than it seems