Event Management Dashboard shown a red tile. When click on the red tile, a relevance Alert record display. When click on the Alert record, it redirected to "Record Not Found" page.
This could happen if a customer accidentally delete the alert record from "em_alert" table via background script.
Event Management Dashboard is referring to "em_alert_history" table.
Go to "em_alert_history" table and find the matching Alert number record. Delete the record from "em_alert_history" table