No Jinja Variables renders in the print preview or PDF output for any Contract Template

I noticed any instance of a jinja variable is not rendering on the print preview or PDF. It just shows the literal variable declaration eg {{start_date}}.

I am following the instructions as per the Contract Template Example:

I have also tried with and without the spaces between the {{ }} just in case but it doesn’t work.

If I set a custom HTML field in the Print Designer and use the same variable declaration it renders fine, but I want to be able to use them in the Contract Template.

Thank you for your help!