a. Ant group is partially owned by a large group of elite foreign investors https://www.wsj.com/articles/ant-ipo-promises-8-billion-gain..., who will gain hugely from this IPO. The Chinese government doesn't want such a huge financial entity owned by foreign owners (even though they have claimed they are allowing more foreign entries in financial sectors). Also, China is suffering from dollar shortage/flight (foreign manufacturing moving out, foreign retailers moving in), and this IPO could exacerbate it
b. Jack Ma recently criticized the Chinese banks https://www.pymnts.com/news/ipo/2020/jack-ma-summoned-for-qu.... This is a big no no right now, especially since Xi's dictatorship is wobbly. Also this is what happens when you upset the world's largest mafia - Chinese government and Chinese state owned companies. Just look at what happened to Australia https://www.abc.net.au/news/2020-11-03/china-broadens-trade-..., South Korea https://www.vox.com/latest-news/2017/3/3/14795636/china-sout... US https://www.defensenews.com/global/asia-pacific/2020/10/26/c... and Japan https://www.nytimes.com/2010/09/23/business/global/23rare.ht...
c. There is probably a lot of financial misreporting within Ant Group, as it is pretty commonplace for Chinese public companies - check out recently delisted Chinese companies in US stock exchanges. If this IPO is allowed to expand, that's game over for shanghai stock exchange sooner than later.
(if you ask me, why would anyone invest in any mafia pyramid scheme with no guarantee you'll get your money out...)