The AddOn is not working as expected. I, currently, have no time for troubleshooting the code. I will eventually fix it. Apologies. Nacho.
Classroom Form Invite does not store any user data. The data is collected and stored by the Form property of the user.
All the permissions that Classroom Form Invite requires are exclusively to perform the functions that have been detailed (read Classroom classes, read form submissions and send Classroom invitations). In no case is the data taken from Google Forms or Classroom. Thus, data security is provided by Google's servers.