The meta key additional_information_0_owner_name is for a repeater and the meta key should be additional_information_owner_name for a sub field of a group field.
This makes me think that your group field is, for some reason, being confused for a repeater. I’ve looked at the code in ACF and there does not appear to be a reason for this and I do not see anything in the code you’ve supplied that should cause this.
I would do this differently, instead of updating the value of this field when it is saved I would populate the value of this field when it is edited because you are doing this update when a post is saved. I would do this using and acf/load_value filter (priority > 10) for the new field. If the value is empty then I’d get the value for the old field and return it.
