Contradiction with Galatians 1:1
This verse emphasizes that Paul's apostleship is not from human authority but by Jesus Christ, which could be seen as differing from the shared nature of the letter in 2 Corinthians 1:1 with Timothy.
Galatians 1:1: Paul, an apostle, (not of men, neither by man, but by Jesus Christ, and God the Father, who raised him from the dead;)
Contradiction with 1 Timothy 2:7
Paul claims to be ordained a teacher and apostle, but some interpret this as emphasizing individual rather than shared authorship or authority as in 2 Corinthians 1:1 where he includes Timothy.
1 Timothy 2:7: Whereunto I am ordained a preacher, and an apostle, (I speak the truth in Christ, [and] lie not;) a teacher of the Gentiles in faith and verity.
Contradiction with Acts 15:39-40
Demonstrates a sharp disagreement leading to separation of Paul and Barnabas, contradicting the cooperative tone with Timothy in 2 Corinthians 1:1.
Acts 15:39-40: And the contention was so sharp between them, that they departed asunder one from the other: and so Barnabas took Mark, and sailed unto Cyprus;