Sentence Correction (SC) | Re: Minnesota is the only one of the contiguous forty-eight states that st

Dear experts,

There is disagreement among experts in whether the original sentence has S-V agreement error or not. Although this doesn't prevent us from identifying the right AC, I would request your help is understanding the point.

Minnesota is the only one of the contiguous forty-eight states that still has a sizable wolf population, and where this predator remains the archenemy of cattle and sheep.
Is has correct here? What is it with "The only one of the Xs that/who" construction