The one I find most reasonable is that you are playing too much chess which makes you lose concentration and you get in a kind of aggressive form in which you will most likely lose. You also don’t get the same thrill when playing. Try getting some fresh air.
Another could be personal problems and the reason is obvious. One more problem could be that you are changing your playing style and not adjusting your time properly. But before playing chess I must advise you, since you said you lost motivation, you need to get some motivation. Think of chess as a game which interests you, even if you lose you are still getting to enjoy the thrill of a game. Try watching some long videos about chess. One YouTube channel I recommend is chess vibes. Specifically the channel’s rating climb videos. Also try playing longer games and take at least one or two minutes before you play a move.
Hope this helps
I've lost over 100 elo. This has made me lose motivation and makes me wanna quit chess.
Does anyone know the reason this could be happening?