With 5.5.0 there are a set of breaking changes that must be considered on new install and/or update.
Digimonitor has been removed
Digimonitor was the old automation engine and that has been removed with 5.5.0. For that reason all existing workflows must be migrated to use the new Automation system.
For many clients this task has most likely been performed already, because the Automation system has been available since Digizuite 5.2.0.
That being said, Digimonitor has historically been responsible for performing system related things. Not all of these things has been moved into the system yet and for that reason the Automation system must do this for a period of time.