How about accidental or unknown sin?
Is accidental sin, willful? Regardless, ask forgiveness and repent. Then ask the Holy Spirit for strength in resisting and overcoming (that) sin.
Unknown sin? Such as? Unknown to you, ever? never to be revealed to you? Maybe something like a sin, that everyone keeps telling you isn’t a sin, and you keep doing it, until you find out it’s actually a sin? Or, as one grows in their spiritual life, they discover that X conduct was in fact sinful? Same remedy as above I would imagine.
If you think there’s anything I missed here, please feel free to comment.