If you are in the free trial plan, and have taken a full length test, then at times, you may not be able to review a few questions here and there.
Sometimes, depending on how you perform on the test, some questions may be required by our algorithm that are not currently available in the free trial. In order to match the exact question type, and difficulty level, the algorithm sometimes picks up questions from our larger pool, which aren't accessible to free trial users.
It happens rarely, and if it happens to you, then you will not have access to those questions that have been picked up from our larger pool.