Two traditional doctrinal conflicts between Catholics and Orthodox have been the procession of the Holy Spirit and the Eucharist Bread.
The Council of Ferrara-Florence (1438-1445) was convened by Pope Eugenius IV for the purpose of reuniting the Greek with the Latin Church who had differing expressions of the faith.
One of these difference was the procession of the Spirit.
Greek Church: The Spirit proceeds from the Father through the Son.
Latin Church: The Spirit proceeds from the Father and the Son.
During the discussion the Greeks admitted that they did not intend to exclude the Son but to indicate that the holy Spirit proceeds from a single principle since the Latin expression "from the Father and the Son seems to indicate two principles of procession of the Holy Spirit. Likewise, the Latins said that they did not intend to exclude the Father from being the source of the Spirit nor to imply that the Son does not receive from the Father. In the end the following definition was agreed upon:
"That the holy Spirit is eternally from the Father and the Son, and has his essence and his subsistent being from the Father together with the Son, and proceeds from both eternally as from one principle and a single spiration. We declare that when holy doctors and fathers say that the holy Spirit proceeds from the Father through the Son, this bears the sense that thereby also the Son should be signified, according to the Greeks indeed as cause, and according to the Latins as principle of the subsistence of the holy Spirit, just like the Father." (ewtn.org/ECUMENICAL COUNCIL OF FLORENCE (1438-1445)
Another difference was in the kind of bread used. In the Church tradition common bread (leavened bread) was used in the celebration of the Lord's Supper up to the 9th century with the exception of the Ebionites and Armenians who who began to use unleavened bread in the 7th Century.
In the 9th Century the Western Church began to use unleavened bread. Why?
Because it was thought that Christ used unleavened bread at the Passover supper
with the Apostles. This was celebrated the day before the Jewish Passover
when the Jews were obliged to get rid of leaven bread from their homes.
2) By using unleavened bread the Church sought to differentiate in the mind of Christians the difference between daily bread and Eucharist bread. This was in conformity with St. Paul words, "Clear up the old yeast, so that you may become a fresh batch of dough, inasmuch as you are unleavened. For our paschal lamb, Christ, has been sacrificed. Therefore let us celebrate the feast, not with the old yeast, the yeast of malice and wickedness, but with the unleavened bread of sincerity and truth." (1Cor. 5:7-8)
The Eastern Church has always used leavened bread and argues that Christ used leavened bread because his Last Supper took place the day before the Jewish Passover. To the Greeks, leaven in bread acted like the soul in the human body giving it life and reminded them of the resurrection. "The Greeks were adamant about the innovation of the Romans. They believed the Latins had left the apostolic faith, they accused them of Judaizing, and of Apllinatianism" (stonedcampbelldisciple.com/The bread on the Table: an Ancient controversy that Changed the Supper)
This council stated: "We define...also, the body of Christ is truly confected in both unleavened or leavened wheat bread, and that priests confect the body of Christ in either, that is, each priest according to the custom of his western or eastern church.". An agreement was reached at the council for unity of Rome with eastern churches but the people never accepted the council of Florence decisions. This led to the Schism of 1054.