Contradiction with Exodus 33:11
This verse describes God speaking to Moses "face to face, as a man speaketh unto his friend," which contrasts with the indirect mode of communication suggested in Exodus 6:29.
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 Numbers 12:8
Here, God says He speaks to Moses mouth to mouth, plainly and not in dark speeches, contradicting the implication in Exodus 6:29 of indirect communication.
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?
Contradiction with Deuteronomy 34:10
States there has not arisen a prophet since in Israel like Moses, whom the Lord knew face to face, contradicting the suggestion of Exodus 6:29 that God's communication was not direct.
Deuteronomy 34:10: And there arose not a prophet since in Israel like unto Moses, whom the LORD knew face to face,