An FAQ answer with [trasl_help_centre] in it is empty

The help centre is not drawn inside an FAQ answer. Drawn there it put a second search box, every topic and the most-read list inside one answer, and all of that into the answer's FAQ structured data as if it were the answer. Write the answer in words and link to your help centre page instead. If you can write articles, you see a note in the answer saying why it is empty; visitors see only the rest of the answer.