Just taking a quick view of the claimants to the Patriarch of Alexandria leading up to the middle of the 6th century, it appears there still were pro-Chalcedon Patriarchs of Alexandria until the early 480’s. For example: Proterius, Timothy Salophakiolos, John Talaia. After this time, for the 55 years up to the election of Theodosius, in 535, the Patriarchs of Alexandria do indeed seem to be nearly all Miaphysite. This period of nearly all Miaphysite Patriarchs largely coincides with the attempt of reconciliation via acceptance of the
Henotikon.
The election of Timothy Auleurus by the supporters of Dioscorus signified the existence of two claimants for the same see. When there was only one Patriarch of Alexandria, it was usually due to the fact that the “previous” Patriarch had either been killed or forcefully booted from the city! Violent times back then!
I do agree that the definitive split took place during Justinian’s reign…
Although, I would add that reconciliation might yet have occurred had not the Muslims conquered Egypt and Syria in the early 7th century.