I’m a fairly new user, but this is basic configuration in WP. If a drop box field has value x then show the single line text field. Without the condition enabled the form shows. With the condition enabled, the preview just shows a blank line and the website just shows an X.
I recreated the form from scratch to prove it was a consistent issue and not due to unseen corruption.
The field (type) used for comparison does not matter. Whether using Hide or Show does not matter.