Your event layout options are incorrect, you should set those to get rid of this message (vem_event_run_dates)
https://www.seoulphil.or.kr/perf/view?perfNo=4009&calendarDate=12/01/2020&langCd=en&menuFlag=MFLG0001
https://www.seoulphil.or.kr/perf/view?perfNo=4009&calendarDate=12/01/2020&langCd=en&menuFlag=MFLG0001