You had a huge (dig) winstreak, played consistent like a challenger but after a while when these winstreaks pass, you get on a lose streak even if you still play consistently, you always lose no matter what you do. This time it is opponents snowballing out of controll.
These games can be tilting and kinda depressing, but even if you decide to reset your mind and play consistent after 5 loses in a row again, you'll still lose and eventually after 8 loses in a row you'll run out of options.
And after these loses pass, you go on a win streak again even if nothing changed on your playstyle. The bad thing about this is that you lose Mmr, I don't personally think that this is how the matchmaking should efficiently be designed. There's a flaw in it one way or another, either it's what people call "The system is trying to keep your winrate at 50%" or there's just in generally fundamentally flawed with who'm I get matched with and against.
I personally think that "Matchmaking is trying to keep your winrate at 50%" is just a myth people made up, I think that Riot simply designed Matchmaking pretty poorly. They're not really open about how it works which is not better since people are creating all these bad myths about it.