The Living Temple contains the alpha of deadly heresies:

I am instructed to speak plainly. “Meet it,” is the word spoken to me. “Meet it firmly, and without delay.” But it is not to be met by our taking our working forces from the field to investigate doctrines and points of difference. We have no such investigation to make. In the book “Living Temple” there is presented the alpha of deadly heresies. The omega will follow, and will be received by those who are not willing to heed the warning God has given. {SpTB02 50.2}

I have been instructed by the heavenly messenger that some of the reasoning in the book, “Living Temple,” is unsound and that this reasoning would lead astray the minds of those who are not thoroughly established on the foundation principles of present truth. It introduces that which is naught but speculation in regard to the personality of God and where His presence is. No one on this earth has a right to speculate on this question. The more fanciful theories are discussed, the less men will know of God and of the truth that sanctifies the soul. {SpTB02 51.3}

CONCLUSION

According to given data, we can give proactive truth driven answer to what constituted the alpha deadly heresies. They were doctrines which lead astray from The Foundation Principles of present truth or The Fundamental Principles specifically on the point on the The presence and the personality of God. So instead of focusing on the error, we should focus on the truth. In this case, this is the doctrine on the The presence and the personality of God expressed in the The Fundamental Principles

Caution, warning

Instead of focusing to the error, we should focus on the truth. The problem with deception is that we can be deceived thinking we are not deceived. We can be fully convinced that we are not deceived, while being deceived,