Contradiction with Matthew 28:19
This verse contradicts with Luke 9:21 as it instructs the disciples to go and teach all nations, openly sharing the message, whereas Luke 9:21 involves Jesus telling his disciples to keep quiet about his identity.
Matthew 28:19: Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: [teach...: or, make disciples, or, Christians of all nations]
Contradiction with Matthew 10:27
This verse encourages proclaiming teachings openly, which contradicts Luke 9:21 where Jesus instructs not to tell anyone about him.
Matthew 10:27: What I tell you in darkness, [that] speak ye in light: and what ye hear in the ear, [that] preach ye upon the housetops.
Contradiction with John 18:20
Here, Jesus states he spoke openly to the world, which is in contrast to Luke 9:21 where he commands silence about his identity.
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.