those are always dicey, as communication was much more porous back then. the Church was able to hold together officially during the Chalcedonian controversy long after Chalcedon. so even if certain saints or writers had heretical leanings, the could still be saints because they were within the Church and holy despite errors
There is also St. Isaac the Syrian, who we now know was probably a member of the Church of the East. Some people dispute the scholarship of Sebastian Brock on this point, and I respect them, but to me, the evidence seems compelling, particularly given that the Assyrians venerate him. Actually all four ancient churches (the Roman Catholics and Oriental Orthodox also venerate St. Isaac). In the case of the Oriental Orthodox this is not as shocking as it might sound, since there were times when relations between the Syriac Orthodox and the Assyrian Church of the East were quite close (including at present; the Assyrians also recently developed a very good relationship with the Moscow Patriarchate).
I am not scandalized by Oriental Orthodox saints being venerated by us; St. John of Damascus is venerated by them. Of course when it comes to EO-OO relations I am about as pro-Oriental Orthodox as one can be, based on the current reality of pan-Orthodox relations in Egypt and Syria.*
The Assyrian Church of the East is a bit more problematic, because despite rejecting Nestorian Christology in favor of a psuedo-Chalcedonian Christology under Mar Babai the Great in the Sixth Century, they still venerate Nestorius, and also for some reason despite denying that they are iconoclasts, they aren’t enforcing their own ancient canon law which requires an Icon of Christ Not Made By Hands to be on every Assyrian altar. They also use the term “Christotokos” which is technically Nestorian. However, at the time of St. Isaac, their main difference with us was an absolute belief that Apokatastasis would happen (this is no longer their position) which is evinced in some of the more recently translated works of St. Isaac.
Of course it is not impossible that Sebastian Brock is in error and has translated someone else and conflated their identities, and there are traditionalists who have identified a possible alternative author also named Isaac, but from my study of the matter, I don’t think he is. I think rather St. Isaac was simply universally recognized as being holy during a period of time when Orthodox-Assyrian relations were particularly good.
*I particularly object to the articles written by Nicholas Marinides on the subject; I would object less if he had also written articles critiquing the Assyrian Church of the East, since both churches are described by Metropolitan Kallistos Ware, memory eternal, as having much in common with us, but since as far as I am aware, in terms of his academic writing, Nicholas Marinides has not done this, it seems like he particularly objects to Oriental Orthodoxy, and my view is that if one objects to reunion with the Oriental Orthodox without also strongly objecting to reunion with the Assyrians, this is an inconsistent approach.
Conversely, I think one can support immediate reunion with the Oriental Orthodox while requiring the Assyrians to make reforms, such as to follow their canon laws requiring the display of icons and to continue the work started by their great Patriarch Mar Dinkha IV, memory eternal, on disavowing Nestorian beliefs, practices and identity.
This is because I prefer the scholarship on this issue of Fr. John C. Romanides, and I believe a confusion existed between the Oriental Orthodox, who deny being monophysites, and the actual Monophysites led by Eutyches, and later by John Philoponus, who taught that the humanity of Christ dissolved into his divinity like a drop in the ocean, and who were anathematized by Pope Dioscorus and the other Oriental Orthodox, and who as one might expect degenerated into Tritheism.
Interestingly, while the heresy of Nestorianism is tragically extremely widespread among Protestants, I can think of only the Mormons as continuing the Monophysite tradition, inasmuch as they are Tritheists (not actual Monophysites, they skipped the intermediate step and just went straight to Tritheism, which is the dead end of the Monophysite road.
