After GP1 rollout, some countries experience a sharp decline in traffic.
This is a phenomenon that occurs due to a change in the cookie consent rate with rules from Onetrust along with GP1.
It is reported that applying Onetrust (Cookie consent mode) reduces traffic by approximately 40-50%.
Reference
04. Traffic 감소 이슈 및 Cookie 동의율 관리 - LG.com Archiving
쿠키 동의율에 따른 GA4 Main 속성 - Sub 속성 데이터 커버리지 검증 - Data Insight Team