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