It can seem strange: commentators revering the same scriptures, each quoting them fluently, arriving at pictures of reality that cannot all be final. No one is being careless. The sources themselves make the disagreement possible. The Upaniṣads speak in many voices; the sūtras that systematize them are so compressed that they rarely settle their own construal; and every commentator accepts all of it as authoritative, which means none can simply discard the passages that favor another reading. Each must instead show how every text fits his interpretation: which statements speak literally and which figuratively, which teach the final truth and which prepare for it.
So the disagreement lives exactly at the level this Atlas is built to show: the same sūtra, more than one commentary, each claiming the whole of scripture for its side. Learn can tell you what each tradition holds. To watch Śaṅkara, Rāmānuja and Madhva diverge, sūtra by sūtra, open any sūtra page and choose Compare commentaries at this sūtra.