Contradiction with Acts 2:1
Acts 1:15 mentions about 120 people being gathered, whereas Acts 2:1 begins with only the apostles being together when Pentecost arrives, without mentioning the larger group.
Acts 2:1: And when the day of Pentecost was fully come, they were all with one accord in one place.
Contradiction with 1 Corinthians 15:6
Paul mentions that Jesus appeared to more than five hundred brethren at once, which is more than the 120 people gathered in Acts 1:15.
1 Corinthians 15:6: After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep.
Contradiction with John 20:19
Describes a meeting where the disciples were assembled behind closed doors due to fear of the Jews, while Acts 1:15 describes a gathering of about 120 people openly in one place.
John 20:19: Then the same day at evening, being the first [day] of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace [be] unto you.