Contradiction with Proverbs 25:2
Romans 11:33 speaks of the unsearchable judgments of God, while Proverbs 25:2 suggests that it is the glory of God to conceal a matter, and the honor of kings to search it out.
Proverbs 25:2: [It is] the glory of God to conceal a thing: but the honour of kings [is] to search out a matter.
Contradiction with Ecclesiastes 8:17
Romans 11:33 emphasizes the depth of God's wisdom and knowledge, whereas Ecclesiastes 8:17 acknowledges man's inability to fully find out the work that God does, despite efforts to seek it.
Ecclesiastes 8:17: Then I beheld all the work of God, that a man cannot find out the work that is done under the sun: because though a man labour to seek [it] out, yet he shall not find [it]; yea further; though a wise [man] think to know [it], yet shall he not be able to find [it].