I’ve been having the same issue since may - and I don’t think there is anything other than different Hik Connect version changes that broke the notification in iOS.
Doorbell: DS-KV6113-WPE1
Firmware: V2.2.53 build 220108 (latest)
Connection type: wired PoE
DNS Server: 8.8.8.8 / 8.8.4.4...