Hello, @Impax.

When you use a template on an invoice and you create another invoice, that template should stay unless you change the template.

In case, the new template doesn't show when you create another invoice, you may have a damaged template.

You can try to recreate the template to resolve the error you’re having. 

Check this article for more information: Fix common issues when you use and customize templates. 

Let me know if there's anything that I can help you with. I'm always here to assist. Have a wonderful day!