If you run MagicMover by a user who has a Profile that was not one that the app was installed to, then additional permissions are required for the permission sets
The VF component NAMPermissionIssue renders the string You don’t have permission to access some fields but the actual exception thrown by NAMUtils.validatePermissions() is eaten by the various controllers such as ATFAttachmentsToFilesController:
try{
NAMUtils.validatePermissions();
}
catch(Exception ex){
permissionIssue = '';
notPermissionIssue = 'slds-hide';
}
This makes determining what permissions are missing challenging. As we move to a Profile-less world and one more driven by users with profile Minimum Access-Salesforce + permission set groups, surfacing the errors would be helpful.