Multiple peers may review a student’s writing submission, depending on your assignment settings. If you see the 'Peers Disagree' button when viewing reviews, student submissions have received reviews that are not in agreement. It could mean that peer reviewers disagreed on every rubric item, or they may only have disagreed on one item:
Navigate to your assignment's Dashboard. Click on 'Grade Now' to see a list of student submissions. Use the grading filters to select "Peers Disagree" to narrow down your results.
Next, you’ll see a list of students’ who’ve received disagreeing reviews. Click on an individual student to see the reviewers' scores and give your feedback, or click 'Start Grading' to go through all of them.
NOTE: Any time you have disagreeing reviews, you should consider reviewing the student submission yourself so as to set the "right answer" for the student reviewers. This will ensure that writers are getting accurate feedback while also ensuring reviewers see how the writing should have been scored.