In the book of Revelation, Jesus has nothing bad to say about the Church of Smyrna or the Church of Philadelphi Are they perfect? Do they ever sin?
They are not perfect and they certainly commit sins. However, they have confessed all of their sins to God (I John 1:9) and hence they are completely forgotten by Him. Hence Jesus does not bring up their failings when He evaluates their faith in the book of Revelation. Their sins will also not be remembered at the Judgment Seat of Christ.