Contradiction with Amos 9:7
This verse suggests that the children of Israel are no different from other nations, while Zephaniah 3:10 implies a special gathering of God's people from afar.
Amos 9:7: [Are] ye not as children of the Ethiopians unto me, O children of Israel? saith the LORD. Have not I brought up Israel out of the land of Egypt? and the Philistines from Caphtor, and the Syrians from Kir?
Contradiction with Isaiah 56:6-7
These verses include all nations coming to worship God, not just a specific group from across the rivers of Ethiopia as mentioned in Zephaniah 3:10.
Isaiah 56:6-7: Also the sons of the stranger, that join themselves to the LORD, to serve him, and to love the name of the LORD, to be his servants, every one that keepeth the sabbath from polluting it, and taketh hold of my covenant;
Contradiction with Acts 10:34-35
Peter states that God accepts people from every nation who fear Him, which contrasts with the specific calling from across the rivers of Ethiopia in Zephaniah 3:10.
Acts 10:34-35: Then Peter opened [his] mouth, and said, Of a truth I perceive that God is no respecter of persons:
Contradiction with John 4:21
Jesus' statement about worshiping God neither on a specific mountain nor in Jerusalem contrasts with Zephaniah 3:10, where a specific group is called to serve God.
John 4:21: Jesus saith unto her, Woman, believe me, the hour cometh, when ye shall neither in this mountain, nor yet at Jerusalem, worship the Father.
Contradiction with Romans 10:12-13
These verses highlight that there is no difference between Jew and Greek, contradicting the specific ethnic gathering implied in Zephaniah 3:10.
Romans 10:12-13: For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.