Contradiction with Numbers 16:40
Numbers 16:40 states that Eleazar the son of Aaron will be in charge of the incense offerings, which implies Aaron is not dead and contradicts the death indicated in Numbers 20:29.
Numbers 16:40: [To be] a memorial unto the children of Israel, that no stranger, which [is] not of the seed of Aaron, come near to offer incense before the LORD; that he be not as Korah, and as his company: as the LORD said to him by the hand of Moses.
Contradiction with Numbers 33:38
Numbers 33:38 mentions the death of Aaron differently when it says he went to Mount Hor, even though it aligns, it presents the event in a broader timeline that differs from the focal point of mourning in Numbers 20:29.
Numbers 33:38: And Aaron the priest went up into mount Hor at the commandment of the LORD, and died there, in the fortieth year after the children of Israel were come out of the land of Egypt, in the first [day] of the fifth month.