The context for the Masoretic text makes sense due to the fact Ahijah the Shilonite was a Levite.
Ahijah is also mentioned earlier in 2 Chronicles 9:29 where it says he wrote a book.
As for the other events of Solomon's reign, from beginning to end, are they not written in the records of Nathan the prophet, in the prophecy of Ahijah the Shilonite and in the visions of Iddo the seer concerning Jeroboam son of Nebat?
Note that the only complete Septuagint texts we have are dated in AD, whereas the oldest Septuagint fragments we have are dated to the mid 2nd century BC. The original Septuagint was a translation of the 5 books of Moses, this was done in the mid-3rd century BC. The rest of the Old Testament was possibly translated into Greek in the 2nd century BC, which raises suspicion. It was most likely translated by other scribes, not the original translators of the LXX (who most likely used Masorah to translate the Septuagint).
The first five books of the Hebrew Bible, known as the Torah or the Pentateuch, were translated in the mid-3rd century BC. The remaining books of the Greek Old Testament are presumably translations of the 2nd century BC.
Several factors led most Jews to abandon the Septuagint around the second century CE.
This text used to be viewed highly by the Jews. Considering the scribes who wrote the rest of the Old Testament (whereas the original LXX was only the 5 books of Moses), the reason for rejecting it later on in history is most likely due to the differences in the text we see today. It's not far off at all to assume the scribes who translated the rest of the Old Testament corrupted it.