Contradiction with John 16:25
John 16:25 mentions that Jesus spoke in proverbs and would later speak plainly, implying that he did not always use parables, whereas Mark 4:33 emphasizes that Jesus primarily used parables to communicate with the people.
John 16:25: These things have I spoken unto you in proverbs: but the time cometh, when I shall no more speak unto you in proverbs, but I shall shew you plainly of the Father. [proverbs: or, parables]
Contradiction with Matthew 11:25
In Matthew 11:25, Jesus thanks the Father for revealing truths to the simple rather than the wise, suggesting direct revelation to some, contrasting with Mark 4:33's idea that he only spoke to the people in parables.
Matthew 11:25: At that time Jesus answered and said, I thank thee, O Father, Lord of heaven and earth, because thou hast hid these things from the wise and prudent, and hast revealed them unto babes.
Contradiction with John 18:20
Jesus states that he spoke openly to the world and taught in synagogues and the temple, where all Jews come together, suggesting openness in contrast to the implication in Mark 4:33 that he spoke only in parables to the masses.
John 18:20: Jesus answered him, I spake openly to the world; I ever taught in the synagogue, and in the temple, whither the Jews always resort; and in secret have I said nothing.