If you want my guess, losing 1,000,000,000 people means bad census data, or…Organ harvesting.
https://en.m.wikipedia.org/wiki/Forced_organ_harvesting_from_Falun_Gong_practitioners_in_China
https://www.nbcnews.com/news/world/china-forcefully-harvests-organs-detainees-tribunal-concludes-n1018646
https://www.bbc.com/news/world-asia-china-55097424
https://www.newsweek.com/us-state-ban-china-organ-transplants-2054849