Contradiction with Matthew 23:9
John 6:59 indicates Jesus teaching in a synagogue to a diverse group, while Matthew 23:9 admonishes against calling anyone on earth 'father', highlighting a different focus in Jesus' teachings.
Matthew 23:9: And call no [man] your father upon the earth: for one is your Father, which is in heaven.
Contradiction with Matthew 13:34
John 6:59 involves a public teaching moment, whereas Matthew 13:34 states that Jesus spoke to the crowd only in parables, suggesting Jesus exclusively used parables in public.
Matthew 13:34: All these things spake Jesus unto the multitude in parables; and without a parable spake he not unto them:
Contradiction with Mark 4:34
John 6:59 seems to suggest Jesus speaking directly, while Mark 4:34 indicates Jesus used parables for the public and explained them privately to disciples.
Mark 4:34: But without a parable spake he not unto them: and when they were alone, he expounded all things to his disciples.
Contradiction with John 18:20
John 6:59 describes a synagogue teaching, while John 18:20 records Jesus saying he taught openly and in synagogues, contradicting any notion of hidden teachings implied elsewhere.
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.