I had a similar problem: The certificate would email notifications to "teachers" who were not assigned to that class. After reviewing all role assignments and finding these users not assigned any teaching roles, I simply set the config to "email teachers - NO" then put the correct email in the "email others" box and it resolved. I still do not know how or why the module selected the other users as "teachers"
Custom certificate (plugin)
Certificate Showing erroneous teachers
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