The problem of variation of manuscripts. We don't have the original manuscripts. What we have are copies. There are variations in the copies. God has entrusted His word to people.
People are imperfect.
For the variations have so little impact on the meaning. And if the objective was for God to communicate meaning, these variations in the manuscripts add up to nothing. It's like complaining about the penmanship of the writer. The Muslims claim that every literal word in the Koran is God-spoken. And therefore a translation of the koran cannot be considered God's word, from the muslim's point of view.