Local Customs: 

Why do some parishes/religious orders include a second Confiteor before the Communion of the Faithful?

While formally omitted from the revision of the rubrics in 1961, the second Confiteor is retained in many places.  This is simply a matter of custom based on what each particular community is used to.  On November 20, 2010, the Pontifical Commission Ecclesia Dei responded that the second Confiteor may be said both at Low Masses and High Masses.