[ OJS] $authorString does not work when add another participants in the Pre-Review Discussions

I am using OJS and try to use OJS for thesis submission,
I choose a predefined message (notification email template) only for the last participant assigned, in here, $authorString works and shows the student name.
Since I want to make it simple and want to invite all the advisors in one pre-review discussion to give the approval, I try to Edit and update discussion and add the other advisor, $authorString seems to works in the discussion, but does not work in the email which send to them.

Need your suggestion. Thanks in advance!