An event chain is configured to send a completion email notification. The event chain is known to complete, but there is no record of that email notification being generated. If the completion is set to Log to Database, the event is logged, but the email is still not sent.
The global threshold setting "Do Not Fire Actions for Messages Older Than" is set lower than the time required for the completion of the event chain.
Increase the threshold setting to a value greater than the maximum expected runtime for the longest event chain in the system. This value is set from the Navigator, Configuration -> Global Settings -> Advanced tab.
This setting prevents an unnecessary dump of event history which previously occurred when a server was first watched. For event chains, this is incorrectly measured from the beginning of the chain and not the end of the chain. A value of 24 hours seems to work well in most settings.