There is another reason why the Protestants rejected the Septuagint. It contains books that are not in the Hebrew text and which contain teachings that cannot be reconciled with Protestantism. For example, 2 Maccabees 12:38-46
Then Judas assembled his army and went to the city of Adullam. As the seventh day was coming on, they purified themselves according to the custom, and they kept the sabbath there.
 On the next day, as by that time it had become necessary, Judas and his men went to take up the bodies of the fallen and to bring them back to lie with their kinsmen in the sepulchres of their fathers.
 Then under the tunic of every one of the dead they found sacred tokens of the idols of Jamnia, which the law forbids the Jews to wear. And it became clear to all that this was why these men had fallen.
 So they all blessed the ways of the Lord, the righteous Judge, who reveals the things that are hidden;
 and they turned to prayer, beseeching that the sin which had been committed might be wholly blotted out. And the noble Judas exhorted the people to keep themselves free from sin, for they had seen with their own eyes what had happened because of the sin of those who had fallen.
 He also took up a collection, man by man, to the amount of two thousand drachmas of silver, and sent it to Jerusalem to provide for a sin offering. In doing this he acted very well and honorably, taking account of the resurrection.
 For if he were not expecting that those who had fallen would rise again, it would have been superfluous and foolish to pray for the dead.
 But if he was looking to the splendid reward that is laid up for those who fall asleep in godliness, it was a holy and pious thought. Therefore he made atonement for the dead, that they might be delivered from their sin.
That gives Biblical support for prayers for the dead, one of the doctrines that Protestants strongly rejected. Therefore, they rejected II Maccabees as part of the Bible because it did not fit into their theological system. One reason the Protestant rejected the Septuagint is that II Maccabees is not found in the Hebrew canon. Luther set the stage for this by rejecting the Epistle of James as an "Epistle of straw" because it taught that faith without works is dead. Luther and all Protestants taught that we are saved by faith alone.
Fr. John W. Morris