Why did Ibn Taymiyyah rule that Fakhr al-Din al-Razi was a disbeliever and an apostate, to the exclusion of other Ash'aris?

Fakhr al-Din al-Razi was a great Ash'ari scholar who mixed philosophy with scholastic theology (kalam), experienced internal turmoil and contradictions, and authored a book on magic and star worship. Ibn Taymiyyah stated that this book of his constituted apostasy and disbelief from Islam. Al-Razi later repented and regretted his engagement with philosophy and kalam, returning to the creed of the Quran and Sunnah and the methodology of the Salaf. Ibn Taymiyyah did not declare al-Razi an absolute disbeliever; rather, he ruled certain aspects of his states and writings as disbelief and apostasy, while also clarifying al-Razi's repentance and return to the truth, and he supplicated for mercy upon him.