My guess is the problem here is not one of mixed voice. Instead, it is a recurring grammar mistake due to pronoun overuse and lack of pronoun reference. This occurs whenever it's unclear who or what the pronoun refers back to. A good rule of thumb is that you should never use more than three pronouns in a row, but even then it depends on the situation. Another way to avoid the problem is the physical distance on the page between the subject's name and the pronoun. If it's more that a sentence or two away you most likely need to state the name again. Sometimes the writer is trying to avoid repeating long or complicated names by using pronouns instead. In this case he or she might choose some simpler, yet clear, replacements, such as the star, the queen, Mr. T., the boss, the protagonist, etc.
The worst misuse of pronouns is when it, that, or this is used to refer to a concept that has not been clearly defined.