Alerter Not Sending to Contacts

Running Version: Observium 19.1.9661 (stable)

None of the contacts configured for the alerter are receiving any alerts. Both Slack and email are configured for three separate contacts.

I have tested running the test_alert.php script in debug against each individual contact and I receive emails it generates successfully.

Forcing an alert to occur causes a trigger and I can see in the `alert_log` table that "Alert notifictation sent" logs are being recorded however it seems that they are not being sent through natural (non-test) alerts.