Actually, I think something like this will only happen in December because we know that in December every club in the EPL is required to do a lot of matches which makes this a little complicated for themselves.
Clubs in the EPL in December sometimes only have a one-day break for recovery and then play again before they get a half-season break.
With a busy schedule every club is required to rack their brains so that the players are not exhausted and their consistency is maintained but sometimes things like this are difficult to happen because after all it will be very difficult to maintain consistency in a situation of busy fixtures that make matches sometimes not too predictable.

But for the case of Manchester United it is more than this because apart from their poor performance the tight schedule further worsens their quality which causes them to be like this now.