From New Catholic Encyclopedia, 2nd. ed., s.v. "Jacob of Sarug (Serugh)," p. 688:
In 1716, E. Renaudot, in his Liturgiarum orientalium collectio, accused James of being a Monophysite. Three years later, J. S. Assemani began publishing his monumental Bibliotheca orientalis in which he argues strongly for the orthodoxy of James. With the publication in 1876 of several key letters, P. Martin seemed to many to have settled the issue: James was a Monophysite. ... P. Krüger has questioned James' orthodoxy; and T. Jansma, in three masterful articles, has proved conclusively that James was a Monophysite of the Severian school and remained so all his life.
T. JANSMA ... "The Credo of James of Sarug: A Return to Nicea and Constantinople," Nederlandsch Archief voor Kerkgeschiedenis 44 (1960) 18–36; "Die Christologie Jakobs von Serugh und ihre Abhängigkeit von der alexandrinischen Theologie und von der Frömmigkeit Ephraems des Syrers," Muséon 78 (1965) 5–46; "Encore le Crédo de Jacques de Saroug," L'orient syrien 10 (1965) 75–88, 193–236, 331–370, 474–510.