App Connect Formatter breaks when input fields display other input fields

I have a hidden field that I update the value dinamically via the press of another button. Another text input field value then displays the value of the hidden field as it is updated.

As soon as I try to format any of the 2 fields as a number with decimals or as a currency, it breaks either before I press the button to update the hidden field or after pressing it once I get NaN.