Contradiction with Leviticus 20:10
While Leviticus 18:14 prohibits uncovering the nakedness of a father's brother, Leviticus 20:10 specifies punishment for adultery more broadly rather than this specific act.
Leviticus 20:10: And the man that committeth adultery with [another] man's wife, [even he] that committeth adultery with his neighbour's wife, the adulterer and the adulteress shall surely be put to death.