Hello,
Please try using the processTemplate method (https://www.phpdocx.com/api-documentation/templates/proccess-a-word-docx-template) after loading a template:
$docx = new CreateDocxFromTemplate('document.docx');
$docx->processTemplate();
We have done some tests generating and loading multiple DOCX in the same script (using and not using the processTemplate method) and everything is working correctly in all cases.
For further support, please send to contact[at]phpdocx.com the most simple code and template that illustrate your issue (without doing external connections such as databases or web services) and we'll check them, maybe there's some issue in the code you are running.
Regards.