Hello,
If PHP throws an out of memory message, it is registered in the log of the server. Do you see that out of memory message in your server logs? Please also test your script using PHP CLI mode.
We have done some tests (doing the merging and working with a single template) with your DOCX and images and everything is working correctly.
Also please run the included samples in the package (LayoutAndGeneral folder: addHeader and addFooter) and check if the images are added correctly.
Regards.