Contradiction with Hebrews 6:4-6
These verses suggest that it's impossible to renew some to repentance after they have fallen away, contradicting the idea that those who do not continue in unbelief may be grafted in again.
Hebrews 6:4-6: For [it is] impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
Contradiction with 2 Peter 2:20-21
This passage states that it would be better for someone not to have known the way of righteousness than to turn away from it after knowing, implying a more severe consequence than the potential restoration mentioned in Romans 11:23.
2 Peter 2:20-21: For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
Contradiction with Matthew 12:31-32
These verses describe blasphemy against the Holy Spirit as unforgivable, contradicting the possibility of being grafted in again if forgiveness cannot occur.
Matthew 12:31-32: Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy [against] the [Holy] Ghost shall not be forgiven unto men.