The document routing agent requires for an Azure token to be generated every 90 days in order to remain operable according to the documentation (and subsequent follow up discussions with Microsoft Support to confirm this), to keep the service working requires several manual steps to be performed by a user - 

Refresh the Azure service token

• Azure authentication tokens must be refreshed every 90 days while the Document Routing Agent is running as a Windows service. To refresh the service token, start the client, and then sign out and sign back in by using the menu items.

https://docs.microsoft.com/en-us/dynamics365/unified-operations/dev-itpro/analytics/run-document-routing-agent-as-windows-service

This is not an acceptable solution for such a business critical function, and should be resolved.