Hi Ben,
Thanks for sending that link! I took a look at the page, and it looks like the field is there, it’s just not being displayed as it should be when the user adds a ticket. This issue is typically related to Javascript, which is responsible for showing the additional fields when the quantity is increased, and is usually due to a conflict with the theme or another plugin. Have you tried deactivating all other plugins and switching to a default theme?
If you are able to confirm this, you can reference this line of code as a possible solution.
Let me know what you find!
Thanks,
Jennifer