Contradiction with Exodus 33:11
While Exodus 19:3 describes Moses communicating with God through an intermediary manner on Mount Sinai, Exodus 33:11 suggests direct communication between the Lord and Moses "face to face, as a man speaketh unto his friend."
Exodus 33:11: And the LORD spake unto Moses face to face, as a man speaketh unto his friend. And he turned again into the camp: but his servant Joshua, the son of Nun, a young man, departed not out of the tabernacle.
Contradiction with Deuteronomy 5:4
This verse states that the Lord spoke directly to the Israelites "face to face in the mount out of the midst of the fire," which contrasts with the depiction in Exodus 19:3 where Moses alone ascends to communicate with God.
Deuteronomy 5:4: The LORD talked with you face to face in the mount out of the midst of the fire,
Contradiction with Numbers 12:8
In this verse, God states that He speaks to Moses "mouth to mouth, even apparently, and not in dark speeches," which suggests a more direct form of communication than the intermediary process suggested in Exodus 19:3.
Numbers 12:8: With him will I speak mouth to mouth, even apparently, and not in dark speeches; and the similitude of the LORD shall he behold: wherefore then were ye not afraid to speak against my servant Moses?