Contradiction with Luke 23:17
The verse is not found in all manuscripts, creating a textual variance rather than a direct contradiction with Matthew 27:15.
Luke 23:17: (For of necessity he must release one unto them at the feast.)
Contradiction with John 18:39
This verse also supports the custom mentioned in Matthew 27:15, about releasing a prisoner at the Passover, corroborating rather than contradicting it.
John 18:39: But ye have a custom, that I should release unto you one at the passover: will ye therefore that I release unto you the King of the Jews?