"After Augustine came Pope Hormisdas, who reigned in the days of the Emperor Justin, when John, Patriarch of Constantinople, was trying to bring peace again to the Church after the aberrations of his predecessor Acacius. Both Emperor and Patriarch accepted the profession of faith of Hormisdas to make it the norm of orthodoxy. Yet that profession contained the following:
'Great and incomprehensible is the mystery of the Trinity. God the Father, God the Son, God the Holy Ghost, an undivided Trinity, and yet it is known because it is characteristic of the Father to generate the Son, characteristic of the Son of God to be born of the Father equal to the Father, characteristic of the Spirit to proceed from Father and Son in one substance of deity' (P.L. 63, 514B)"
I may be mistaken but I believe St. Mark of Ephesus refused to accept this. In other words, as with the Didache, it is of questionable provenance. Being of questionable provenance, it is unworthy of consideration other than as a curiosity of some sort. Sort of like an unusual dead rat.
"The words of the western Fathers and Doctors, which attribute to the Son the cause of the Spirit, I never recognize (for they have never been translated into our tongue nor approved by the Oecumenical Councils) nor do I admit them, presuming that they are corrupt and interpolated ..."
PS: Note that while Mark insists that the Son isn't the cause of the Spirit, Gregory of Nyssa says that he is (Against Eunomius, I, 42).
But what made it questionable other than it was evidence that went against his position? The facts remain and we cannot deny them because they are inconvenient.