Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Ensure that who, which, and that take verbs that agree with their antecedents
Make subjects and verbs agree
Grammar

Like most pronouns, the relative pronouns who, which, and that have antecedents, nouns or pronouns to which they refer. A relative pronoun used as the subject of a subordinate clause takes a verb that agrees with its antecedent.

One of the

Constructions such as one of the students who [or one of the things that] cause problems for writers. Do not assume that the antecedent must be one. Instead, consider the logic of the sentence.

Only one of the

When the phrase the only comes before one, you are safe in assuming that one is the antecedent of the relative pronoun.