I'm totally not sure. And my idea of the debate came from my increasingly poor and muddled memory conflating Nicaea with an apparently previous debate which had one of the church fathers (I can't remember who) being ultimately the last defender as, one by one, other fathers were persuaded against its divine origin, and he, too, gave up on the notion. That was well before Nicaea, from what I can tell now. I was not familiar with the Synodicon of Vetus at all (so that should tell you of my level of knowledge on church history); however, looking it up, Wikipedia (and I know that's far from an infallible source) said some interesting things about Nicaea in its article about the S of V. :

The Synodicon Vetus is also the only ancient source that asserts the canonical books of the Bible were decided at the First Council of Nicaea. French Enlightenment writer Voltaire popularized the idea in the 18th century, and Christian radical Robert Taylor revived it in the 19th, but all instances of this assertion seem to trace back to the Synodicon Vetus. Modern scholars reject this notion, and consider the development of the Christian biblical canon to have evolved over centuries. https://en.wikipedia.org/wiki/Synodicon_Vetus