we are facing a new issue with notifications since last release.
notifications used to pop for every message received. now when multiple messages, from the same source, are received. it seems only the last one is poping in the notification area. so users know there are messages waiting but only the last one is actually been displayed in the notification panel.
I asked developers about this and they said they also could not reproduce this. They suggested that perhaps the notifications are being grouped by the OS, but tapping on the notification should expand all of them.