The DE server may not come up after a restart or changerole due to a new application that was added or imported. An error like this is observed in the tracelogs:
Release : 12.x
Component : CA WORKLOAD AUTOMATION DE (DSERIES)
If a new application was added or imported with a Link job, then it may have incorrect XML tags for Link and Task jobs. The Link job may have Failure code with email specified. This is not a valid tag for DE (ESP dSeries) and will result in null exception.
Note: The DE service will shutdown (crash) only on restart as the server will try to reprocess the application again in the active tables.
A cold start is required to clean up the active tables of incorrect Link jobs. The application will then need to edited. Delete the current link jobs and recreate them. This will add the link jobs with correct XML tags.