No reputable scholar denies the authenticity of St. Clement’s Letter to Rome or St. Ignatius of Antioch’s 7 epistles. Lightfoot, Von Harnack, Zahn and Funk accept them. The reason they were questioned because of there Catholicity.
Philip Schaff in his introductory note finally now only questions whether the Longer or shorter Greek versions or Syriac version is the most accurate one. The question of whether they are not authentic is only still found in American Fundamentalist circles.
http://www.ccel.org/ccel/schaff/anf01.ii.i.html
http://www.ccel.org/ccel/schaff/anf01.v.i.html
Philip Schaff died in 1893...