You can test your notification Rules by setting the “Maximum number of check attempts for host” or “Maximum number of check attempts for services” for a specific host/service to “1”.
Proceed “Fake Test Results” for this host or service.
Check the “matches” and “no mtaches” in “/opt/omd/sites/sitename/var/log/notify.log”
This gives a hint, why a notification is send or not send.