I GOT DEMOTED BY A REMAKE?

Were you queued with the guy that caused the remake?

You must've been on the brink of losing masters.

"PENALTIES

If you're the inactive player in a match, you'll receive the following penalties:

A loss on your record; if you were in a promo series, you'll lose one game towards it. LP loss, just as though you'd lost the match. Your account will be flagged by LeaverBuster, the same way as if you'd disconnected from a normal match. For Diamond V and above, if someone in your premade is the cause of a /remake, you'll take the same penalties they do. We may adjust this restriction in the future. "

Are you in D5 or higher?

when you queue with a leaver at high elo you lose Lp too. its in the description

For Diamond V and above, if someone in your premade is the cause of a /remake, you'll take the same penalties they do. We may adjust this restriction in the future.

Take the L for trying to dodge a game with your duo