Time, Gentlemen, Time !

They say, one day you look in the mirror and you're old. I say that everal times a week I look at a live blitz game and my time is "old" eg 0:00 with my opponent still having well over 1 minute left, often much more. I posted this topic before and the most believable explanation was internet or time lag, between me entering a move and before it is registered by the chess.com computer. However I see no "lag" or delay when I enter a move, it is instant on the screen, my opponent and I play at definitely even speeds (sometimes I am even faster), and suddenly 0:00 kicks in. Why ?

I have been trying to have a similar query addresed for 15/10 games. When playing opponents of similar ability , their clock moves down a minute compared to my 10.