Regarding osTicket Awesome, there is nothing that should change the way templates work.
When problems such as this arise, the first step is to always isolate whether or not it is actually an issue with osTicket Awesome.
Do you still have your original osTicket installation? As per the installation instructions I recommend holding onto it for situations like this.
RBGE in the osTicket forum is recommending the same thing. He is using the term “clone” installation. I would call it a “parallel” installation. If you didn’t keep a parallel osTicket installation, you can easily add one.
Assuming you have osTicket Awesome installed into a folder named support/, upload the osTicket (v1.12?) files into a folder named support-old/.
Copy support/include/ost-config.php to support-old/include/.
Visit your core osTicket installation by going to http://www.yourdomain.com/support-old/scp and troubleshoot your email templates.
If it turns out that it is an issue with osTicket Awesome, let me know!