Contradiction with Matthew 10:5
This verse instructs the disciples not to go to the Gentiles, which contradicts the instruction given to Peter regarding Cornelius, a Gentile, in Acts 10:5.
Matthew 10:5: These twelve Jesus sent forth, and commanded them, saying, Go not into the way of the Gentiles, and into [any] city of the Samaritans enter ye not:
Contradiction with Galatians 2:12
This suggests an earlier tension between Jewish and Gentile believers, in contrast to the outreach to Gentiles prompted by the vision in Acts 10.
Galatians 2:12: For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.