Contradiction with Leviticus 10:1
Nadab and Abihu offering strange fire was not accepted by God, contradicting the idea of a prescribed joyful celebration in Nehemiah 12:27.
Leviticus 10:1: And Nadab and Abihu, the sons of Aaron, took either of them his censer, and put fire therein, and put incense thereon, and offered strange fire before the LORD, which he commanded them not.
Contradiction with 2 Samuel 6:7
Uzzah was struck dead for touching the ark, which contrasts with the joyful assembly and celebration in Nehemiah 12:27.
2 Samuel 6:7: And the anger of the LORD was kindled against Uzzah; and God smote him there for [his] error; and there he died by the ark of God. [error: or, rashness]
Contradiction with Amos 5:21
God expresses hatred for festivals and assemblies, which contradicts the celebration called for in Nehemiah 12:27.
Amos 5:21: I hate, I despise your feast days, and I will not smell in your solemn assemblies. [in...: or, your holy days]
Contradiction with Isaiah 1:13-14
God denounces sacrifices and festivals, conflicting with the joyous dedication ceremony in Nehemiah 12:27.
Isaiah 1:13-14: Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; [it is] iniquity, even the solemn meeting. [iniquity: or, grief]