In some circumstances, a Tasklist Automator can become invalid. This is indicated by the color of the Automator, once you have created it.

A valid Automator appears grey, and will trigger without any issues.

If your Automator displays a warning in orange, it indicates that the scenario is not ideal but will still work. 

Example: The Automator will assign a section of tasks to a job role, rather than to an individual team member

If you are unsure why the warning is displayed, open the Automator to reveal the cause of the warning and a suggested solution.

A red warning indicates that an Automator is invalid, and will not work.

Example: If you move a section of tasks to the top, containing an Automator to change the assignee when the tasks above move into the status of 'Completed', is renders that Automator impossible.