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