Contradiction with Exodus 14:22
This verse contradicts Psalms 77:20 as it mentions the Israelites walking through the sea on dry ground, unlike being led by shepherds on land.
Exodus 14:22: And the children of Israel went into the midst of the sea upon the dry [ground]: and the waters [were] a wall unto them on their right hand, and on their left.
Contradiction with Deuteronomy 1:33
This verse implies the Lord led the way through the wilderness by a visible presence of fire and cloud, contrasting with the image of leading like a shepherd in Psalms 77:20.
Deuteronomy 1:33: Who went in the way before you, to search you out a place to pitch your tents [in], in fire by night, to shew you by what way ye should go, and in a cloud by day.
Contradiction with Isaiah 40:11
This verse suggests God Himself will feed His flock like a shepherd, whereas Psalms 77:20 refers to Moses and Aaron leading them.
Isaiah 40:11: He shall feed his flock like a shepherd: he shall gather the lambs with his arm, and carry [them] in his bosom, [and] shall gently lead those that are with young. [that...: or, that give suck]