As for non-Jeromian authorship, I don't quite understand Rivetus' argument. I can't find any modern textual scholars that take that position. It is a major commentary on Galatians, of which no other writers from that era are known or said to have composed. Also, the author certainly takes the aberrant position of Jerome on Gal. 2:11-14, that Augustine so ardently opposed, with the later having cited parts of Jerome's commentary that match this one during the prolonged correspondence between the two over that matter.