Contradiction with Matthew 24:36
This verse states that no one knows the day or hour of the end, seemingly contradicting Luke 21:31's implication of knowing the approach by signs.
Matthew 24:36: But of that day and hour knoweth no [man], no, not the angels of heaven, but my Father only.
Contradiction with Acts 1:7
Jesus tells his disciples it is not for them to know times or seasons, which appears contrary to Luke 21:31's suggestion of discernible signs for the kingdom's approach.
Acts 1:7: And he said unto them, It is not for you to know the times or the seasons, which the Father hath put in his own power.
Contradiction with 1 Thessalonians 5:2
This verse likens the coming of the day of the Lord to a thief in the night, contradicting the idea in Luke 21:31 that signs make the timing evident.
1 Thessalonians 5:2: For yourselves know perfectly that the day of the Lord so cometh as a thief in the night.
Contradiction with 2 Peter 3:10
It states the day of the Lord will come unexpectedly, unlike Luke 21:31's portrayal of signs indicating it.
2 Peter 3:10: But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.