Contradiction with Matthew 17:9
Contradicts by instructing not to tell the vision to anyone until the Son of Man is risen, whereas Luke 9:36 mentions they kept it secret without specifying any condition.
Matthew 17:9: And as they came down from the mountain, Jesus charged them, saying, Tell the vision to no man, until the Son of man be risen again from the dead.
Contradiction with Mark 9:9
Contradicts by giving a direct command from Jesus to not mention the transfiguration until the resurrection, contrasting with Luke 9:36's note of silence without detail.
Mark 9:9: And as they came down from the mountain, he charged them that they should tell no man what things they had seen, till the Son of man were risen from the dead.