Chris-Wa1, yes, the Book of Mormon disagrees with later Mormon doctrine. But they just reinterpret it. I have asked Mormon missionaries, how come that the Book of Mormon says the Father , Son and Holy Ghost are one God (2 Nephi 31:21, Alma 11:44, 3 Nephi 11:27, Morm. 7:7), and you teach they are 3 Gods, and they answered me that in a way they could be considered one God, since they are united in purpose, doctrine etc. and are Almighty, but to be really correct they are 3 Gods.
At least I haven’t seen any clear internal doctrine or other contradictions in the Book of Mormon, though the English grammar is erratic, mostly the KJV grammar, but sometimes modern English grammar.
On the other hand, the Bible has many contradictions, including many doctrinal contradictions, especially in the New Testament, for example in Matthew Jesus is quoted as saying we need to baptize in the name of the Father, the Son, and the Holy Spirit, but in the book of Acts, for example in 2:38, Peter is quoted as saying that what they had to do is repent and be baptized in the name of Jesus Christ for the remission of sins. And similarly other verses in Acts. So some churches baptize in the name of Jesus, and they interpret Matthew as meaning that the name of the Father, the Son and the Holy Spirit is Jesus, at least that is the usual doctrine of almost all Oneness Pentecostal denominations. But most churches baptize according to the Matthew formula, and they might claim that the references to the baptism in the name of Jesus were incomplete, that in reality they baptized in the name of all 3 persons. So they reinterpret this doctrinal contradiction in the Bible, to make the Bible not contradict. And likewise with many other doctrinal contradictions in the New Testament. No wonder there are so many doctrinal differences among Christian churches. Including Mormon churches, for example different interpretations of baptism for the dead, and also a few non-Mormon churches have baptisms for the dead, for example the New Apostolic Church. At least as far as I know, such baptisms are done only in churches that believe that water baptism is necessary for salvation, so they provide it also to the dead who died unsaved and unbaptized.