Contradiction with Numbers 21:24
It contradicts Joshua 12:17 by narrating the defeat of king Sihon by Israel, whereas Joshua 12:17 lists it among kings conquered by Moses.
Numbers 21:24: And Israel smote him with the edge of the sword, and possessed his land from Arnon unto Jabbok, even unto the children of Ammon: for the border of the children of Ammon [was] strong.
Contradiction with Deuteronomy 3:21
It contradicts by emphasizing Moses and the possession of the region, differing from the conquest emphasis in Joshua 12:17.
Deuteronomy 3:21: And I commanded Joshua at that time, saying, Thine eyes have seen all that the LORD your God hath done unto these two kings: so shall the LORD do unto all the kingdoms whither thou passest.
Contradiction with Joshua 13:10
This verse contradicts Joshua 12:17 by detailing differing territories and their control status after conquest.
Joshua 13:10: And all the cities of Sihon king of the Amorites, which reigned in Heshbon, unto the border of the children of Ammon;