international student visa rejection Korea student visa instability Korea international student immigration review Korea student visa after graduation d-10 visa korea job seeking visa korea student visa korea attendance work rules international student korea immigration student visa korea attendance rules student visa document mistake Korea student visa pattern issues Korea university change immigration Korea student visa korea rules international student korea immigration attendance korea international student job rules korea student part time work korea visa student visa attendance rules Korea international student administrative risk Korea international student visa korea problems international student attendance Korea hikorea d10 student visa transfer Korea