No doorbell HomeKit notification on my iPhone (but got them on my iPad)

We installed an Aqasa G4 doorbell with HomeKit. The notifications pop up on Apple TV, on both our iPads and on the Home Pods Mini, but they do not pop up on either of our iPhones.

The doorbell is otherwise fully functional on the phones' Home app (can see the stream, talk, ...), except the phones’ notifications.

Everything is up to date, restarted, removed and re-paired, ...