All I can really give you is what I posted about this subject when I was attempting to do it.
You need to create an acf/load_value filter priority > 10. At this point the ACF value might be the unserialized version of the value, you will need to test this by var_dump($value). You might be able to correct the value at this point. If not then you need to use get_post_meta() to have WP get the value. This value will also be the unserialized value. WP automatically unserializes data when it is retrieved. Depending on the values that you get you then need to serialize it correctly so it matches what you want it to be and return the correct value from the filter.
You’ve basically got to undo what WP has done to the value so that it appears in the text field correctly.
