You should use premoves when playing blitz (I checked only 1 game, but you didn't use any).
Premoves take only 0.1 seconds off the clock.
It's so fast the sometimes it will look like your opponent's time is counting down, but then the server tells your computer it was a premove, and it will look like their timer goes up. In other words they're not gaining time, it's a lag issue with chess.com servers.
I usually play 3 min games without increments, but sometimes when me and my opponent have 10 seconds at the end of the game and my opponents start to check me, their times increase!!!! I dont know why! If you cannot manage your time change the time of the game why would “chess.com” let this happen! So disappointed..