Contradiction with Judges 2:10
It describes a generation that did not know the Lord nor the works He had done for Israel, contradicting the idea of continued faithfulness in Joshua 24:31.
Judges 2:10: And also all that generation were gathered unto their fathers: and there arose another generation after them, which knew not the LORD, nor yet the works which he had done for Israel.
Contradiction with Judges 2:12
This verse notes that the Israelites forsook the Lord to follow other gods shortly after Joshua's generation, contradicting the sustained worship described in Joshua 24:31.
Judges 2:12: And they forsook the LORD God of their fathers, which brought them out of the land of Egypt, and followed other gods, of the gods of the people that [were] round about them, and bowed themselves unto them, and provoked the LORD to anger.