It is something that was there and you found it. The issue is that the fields in both cases are actually named the same and stored in the database under the same meta key, as you have found. This is due to the way that ACF names different field types.
For normal fields it is simply the name of the field “hero_title”
Now you have a group field and the way these are names is "{$field_name}_{$sub_field_name}". Unfortunately this results in the same field name “hero_title”.
You will need to rename either the field or the sub fields.
