is_unique issue on update

Actually I'm getting similar issue...validation works partially or not as intended...
I've a form with two fields. If I change both fields, the validation is ok. If I change only one field, validation blocks the code.

PHP Code:

protected $validationRules      = [
        'group_name'      => 'required|min_length[3]|max_length[50]|is_unique[groups.group_name,group_id,{group_id}]',
        'group_sigla'       => 'required|min_length[2]|max_length[5]|is_unique[groups.group_sigla,group_id,{group_id}]',
    ];