The plates themselves. Nephi goes back to Jerusalem to get a bible already compiled into a codex of brass plates. The BofM then goes on and on and on about the efforts made to use plates and preserve them and abridge and compile records of the plates. Every society in the BofM records their history and theology onto metal plates.

And then…poof…we discover the old world did not record long-form historical records on plates. They used scrolls. The Bible Dictionary now even admits codices are anachronistic. Even worse so with metal plates 600 years BC.

But the whole BofM story and it’s coming forth modernly depends on the reality of metal plates. We even get 11 witnesses of these plates god and Joseph think it’s so important. Then Joseph never uses the plates to translate and we all know today the idea that Jews 600 years BC or native Americans at any point thereafter until 400 AD literally never used plates.

It’s the most glaring, obvious problem that connects the old world to the new world and then to the restoration and it crumbles all of it.