Contradiction with Genesis 13:7
This verse describes strife between the herdsmen of Abram and Lot, illustrating division, whereas Ezra 6:21 speaks of unity in seeking the Lord.
Genesis 13:7: And there was a strife between the herdmen of Abram's cattle and the herdmen of Lot's cattle: and the Canaanite and the Perizzite dwelled then in the land.
Contradiction with Exodus 12:43-45
These verses prohibit foreigners from eating the Passover, whereas Ezra 6:21 includes all who separated themselves to seek God.
Exodus 12:43-45: And the LORD said unto Moses and Aaron, This [is] the ordinance of the passover: There shall no stranger eat thereof:
Contradiction with Deuteronomy 23:3
This verse forbids Ammonites or Moabites from entering the assembly of the Lord, while Ezra 6:21 allows those who separate themselves to join in.
Deuteronomy 23:3: An Ammonite or Moabite shall not enter into the congregation of the LORD; even to their tenth generation shall they not enter into the congregation of the LORD for ever:
Contradiction with Nehemiah 13:3
This verse shows the exclusion of mixed multitude, contradicting the inclusivity seen in Ezra 6:21.
Nehemiah 13:3: Now it came to pass, when they had heard the law, that they separated from Israel all the mixed multitude.