Contradiction with Exodus 12:20
Command not to eat anything leavened; Joshua 5:11 mentions eating unleavened cakes.
Exodus 12:20: Ye shall eat nothing leavened; in all your habitations shall ye eat unleavened bread.
Contradiction with Deuteronomy 16:8
Specifies six days of eating unleavened bread; Joshua 5:11 details eating unleavened cakes immediately after Passover.
Deuteronomy 16:8: Six days thou shalt eat unleavened bread: and on the seventh day [shall be] a solemn assembly to the LORD thy God: thou shalt do no work [therein]. [solemn...: Heb. restraint]
Contradiction with Leviticus 23:6
The Feast of Unleavened Bread starts on the 15th day, but Joshua 5:11 mentions eating unleavened cakes on the day after Passover.
Leviticus 23:6: And on the fifteenth day of the same month [is] the feast of unleavened bread unto the LORD: seven days ye must eat unleavened bread.