It started with McDermott and his vision of what the offense should be not what it was with Dabol. I think Mcdermott wanted to slow it down and call plays like Mac Jones was the quarterback and not Josh Allen in his prime . And for whatever reason Diggs was not the same guy last year. Frustration from the playcalling and targets ? And Allen doesn't call the plays. They lost to KC by 3 last year and a missed field goal. Its not like they got blown out by KC. And the 13 second game that Allen had won until Mcdermott and / or Frazier blew it. And they came back from an impossible position to win their division . And the play calling during and at the end of the game was not great . They needed to put up more points not play not to lose . In any event more likely than not it will come down to the Bills and the Chiefs next year.
