Contradiction with Acts 9:27
Barnabas took Saul to the apostles in Jerusalem, whereas Acts 20:4 mentions a group traveling but not going to the apostles.
Acts 9:27: But Barnabas took him, and brought [him] to the apostles, and declared unto them how he had seen the Lord in the way, and that he had spoken to him, and how he had preached boldly at Damascus in the name of Jesus.
Contradiction with Galatians 2:1
Paul went to Jerusalem with Barnabas, not listed in Acts 20:4 among companions.
Galatians 2:1: Then fourteen years after I went up again to Jerusalem with Barnabas, and took Titus with [me] also.
Contradiction with Acts 15:39
Paul and Barnabas separated, contrasting with the unity in companionship seen in Acts 20:4.
Acts 15:39: 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;
Contradiction with 2 Timothy 4:10
Demas is mentioned as forsaking Paul, unlike the supportive presence of companions in Acts 20:4.
2 Timothy 4:10: For Demas hath forsaken me, having loved this present world, and is departed unto Thessalonica; Crescens to Galatia, Titus unto Dalmatia.