Problem
Custom incident description tags are not being replaced by the values from the event.
Solution
Tags are only available for events that are indexed by New Relic.
The easiest way to know whether an event is indexed is to run the query SELECT nr.entityType FROM ${EventSampleName}, replacing ${EventSampleName} with the name of the event in question.
If there are values in the column nr.entity Typeย of the result, then the event is indexed. Otherwise it is not.
Cause
It is not possible to add a description to any sample that does not get indexed in New Relic.