Hi @Adam Ainsworth
If the field has not been saved to the post, then it is not possible for ACF to find the correct field object or field_key.
You will need to use pass in the field_key to the $field_name parameter of your function. Please note that the get_field_object function will work correctly using the field_key.
By using the field key, the field object will always be found.
I hope this helps
Cheers
E