Contradiction with Exodus 20:3
Numbers 29:20 prescribes offerings to God, whereas Exodus 20:3 emphasizes worship of no other gods, but could be viewed as contradictory in the sense of focusing on ritual rather than exclusive devotion.
Exodus 20:3: Thou shalt have no other gods before me.
Contradiction with Isaiah 1:11
While Numbers 29:20 details offerings for a feast, Isaiah 1:11 conveys that God takes no pleasure in burnt offerings and sacrifices, suggesting a contradiction in the importance of such rituals.
Isaiah 1:11: To what purpose [is] the multitude of your sacrifices unto me? saith the LORD: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats. [he goats: Heb. great he goats]
Contradiction with Psalm 51:16
Numbers 29:20 details specific sacrifices, while Psalm 51:16 notes that God does not delight in sacrifice, questioning the necessity of the offerings described.
Psalm 51:16: For thou desirest not sacrifice; else would I give [it]: thou delightest not in burnt offering. [else...: or, that I should]