Or your opponent trolled you by playing 67...a3 making you think you can mate. 
Maybe I'm just unlucky, but hope it can be fixed!
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Quote from the help section: "Chess.com ignores the material your opponent has when determining if you have sufficient material for a mate."
It's not satisfying.
Lol, I had that too, one game that I should have won when the opponent flagged and one game that the opponent should have won when I flagged. Guess it kinda breaks even, but they should probably fix it.
Oh never mind my example is probably different
ccohho wrote:
I drew this game as white, although I was about to mate in one! My opponent, also knowing there was a mate in one, managed to draw the game by waiting for his time to drop, in which the system believes it is insufficient material and I am unable to win.
I hope this problem can be solved, and that insufficient material will only be shown to situations where there is completely no mate for all legal moves.
https://www.chess.com/live/game/4426929702
That situation is in the the minority of timeout draws, but you could always open a ticket to support since the win was forced.
https://support.chess.com/article/346-contact-us
Let’s see - two players from the same country, both confidently whipping out 20+ moves of mainline hedgehog theory in 3/2 blitz, culminating in a very unlikely ‘unlucky’ finish.
By contrast, an earlier game between the same players culminated in a 2 move fools mate.
Let’s just say I’d be shocked if that game is unique.
I drew this game as white, although I was about to mate in one! My opponent, also knowing there was a mate in one, managed to draw the game by waiting for his time to drop, in which the system believes it is insufficient material and I am unable to win.
I hope this problem can be solved, and that insufficient material will only be shown to situations where there is completely no mate for all legal moves.
https://www.chess.com/live/game/4426929702