I have the same issues.
I’m running two Installations. The first one has only one user which receives two notifications, the second has two users which receive three notifications every time.
In both cases the notification rule is set to only notify those specific users but in the notify.log i can see two/three identical messages.
I did a plain installation of cmk cre 2.2.0p3 on a test system. Notifications worked as expected.
So i guess it must be some setting in the upgraded installations causing the issue which isn’t very obvious.