Symptoms

Worklist is invalid or no longer present
 

Diagnoses

It may happen when ActionersName value of the affected user in the Server.Actioner table in the K2 DB contains a trailing space which is causing this issue.
 

Resolution

This can be resolved by running the following SQL query against the K2 DB:

-- Be sure to backup K2 DB before running this query

UPDATE Server.Actioner SET ActionerName = rtrim(ActionerName)

This query will remove the trailing space. Do remember to always create a backup of the DB first for rollback purpsoses.