Korean university visa student visa instability Korea hikorea d10 student visa after graduation student work permit Korea student visa korea attendance rules part-time work Korea student visa attendance rules Korea student visa transfer Korea international student visa korea problems student attendance Korea student visa korea rules international student korea immigration attendance korea international student administrative risk Korea student visa korea attendance work rules international student korea immigration international student attendance Korea D-2 visa Korea student part time work korea visa part-time work Korea international students international student visa rejection Korea student visa Korea student visa document mistake Korea international student Korea study in Korea university change immigration Korea international student immigration review Korea D-4 work permission student visa pattern issues Korea international student job rules korea D-2 part-time job job seeking visa korea d-10 visa korea