In Mainland China, the sudden interference of the government is attributed to the discovery of the stake of Jiang Zemin’s faction in Ant Group. It’s not a direct stake, but obfuscated through a chain of ownerships.
JZM’s faction is nowadays widely seen in Mainland China as being full of corruption and selfish agenda. Naturally, President Xi doesn’t want to see the influence of JZM’s faction over something as large as Ant Group, so the government decided to halt the IPO before it got too big.