I'd bet that looking through the game log of those games where Allen's defense was considered to have "choked" at the end of the game that a significant majority of them have one or more things in common:
a.) either the offense was playing small ball and going into a shell leading to either a "run-run-incomplete pass-punt" drive or a "run-incomplete pass-incomplete pass-punt" drive leaving even more time for the opposing team;
b.) the game was within one score (driving to go up 2 scores) or tied and the offense coughed the ball up early in the drive forcing the defense back out onto the field with little to no rest (usually right after they had gotten their own stop or turnover);
c.) the defense was holding the opposing team to ~20 points or less the majority of the game and could no longer hold and finally broke
From 2006-2016 it was mostly a mix of A and B, but since Allen turned the defense around it's been a lot of B and mostly C.