When you’re viewing an item, only the fields which are populated are visible.
This is because we spend more time reading issues than editing them. You can add a hidden field at any time by going to the Item Menu and adding the field directly from there:
Always Visible/Hidden Fields
You can also mark a field to always be displayed or hidden, regardless of whether it contains any content or not.
To mark a field as always visible, go to the Item Menu > Always Visible Fields and select your field from the submenu displayed there.
To mark a field as always hidden, go to the Item Menu > Always Hidden Fields and select your field from the submenu displayed there.