if renaming the field corrected it then these are the only possible explanations.
1) There was a conflict with some other field. This field could be an ACF field or any other field created by any other plugin or WP
2) There was a stray value somewhere in the database saved using that meta_key “tagsagiforma” that was not deleted correctly when the value was updated. Do to the way ACF stores and gets values if this meta_key exists more than once only the oldest saved value will be retrieved by ACF.
