someone wins match without checkmate or time run out
It could be due to disconnection or abandonment.
https://support.chess.com/article/338-how-does-game-abandonment-work
https://support.chess.com/article/4720-online-chess-performance-optimizations
It's also possible there was an outage that caused one of the above. If it's one of your games, you can submit a ticket with support including a link the the game. If it coincided with a downtime, support may be able to provide a rating refund.
https://support.chess.com/article/346-contact-us