Hi there,
Thank you for reaching out. Could you please check the following settings in your Joomla admin?
Go to Global Settings > SP Author Archive > Display Options > Set it to All Authors.
like this: https://prnt.sc/RUusddw97155
I have tested the template, and all(13) authors are displaying correctly on my end.
If the issue persists after making this change, please share the admin credentials in the hidden content box for further investigation. Additionally, ensure you create a full site backup using Akeeba Backup before sharing the credentials.
Best regards