Site not adding teacher for my student

I'm a parent. When logged under my credentials, the site will not add my chosen teachers email to my student's username. However, it will add these same teachers to my own learner's page. Originally, I added teachers (for my student) to my learner profile inadvertently. I then added them to my student's username. I inadvertently deleted them from the student profile (instead of mine) and the site will not add them again. However, I can delete and add the same teachers to my learner's profile without a problem.