Why does the game start before everyone has loaded in?

This has happened quite a bit recently, and I know for sure it's not my PC nor internet because almost all of my friends have experienced this at least once in the past month.

Basically, you'll be in the loading screen (usually at 75-90%) and the game will start. The only reason I know the game starts is because I frequently play with friends who tell me it does. The game then thinks you're actually in the game but in reality, you're still loading. So minutes can go by before you get into the match.

So what happens when you're still loading and 3 minutes have passed? Remake.

-50 LP.

obviously, this is incredibly frustrating since there is nothing you can do to fix it. It's entirely up to Riot.

I have no clue if the bug is known or if Riot is working on it, but after getting demoted a rank, I had to post something.