a) After Jeff talked to his brother about the project, he went home.
In sentence a, there is a pronoun reference (REF) problem. Pronouns are used to stand for or to take the place of a noun and they should clearly refer to that noun (the antecedent).
When pronoun reference is faulty, there is a pronoun reference problem just as in sentence a. In this sentence, it is not possible to know whether the pronoun refers to Jeff or to his brother.