A Co-teacher may report that they cannot access their assigned course/class in School Loop and that they are unable to see the co-teacher's buttons for editing classrooms and gradebooks, although they've been authorized by the teacher.
You will need to reach out to the Teacher of the said course and make sure that they've properly added you as a co-teacher and assigned you the correct course rights as mentioned in the article Adding a Co-teacher. This issue could be due to the fact that you have two different accounts in School Loop and the teacher is providing the rights to the wrong account so make sure they select the right one.
Please note that co-teachers will still not have the right to publish the grade reports. Only the original teacher can perform this action.