Hi @David ,
You mentioned "Update Management Center" which is not leveraging AzureHybrid workser service (I assume you are referring to Azure Hybrid Worker server roles).
It means you may have configured Update Management (not Center!) which is version 1 of Update Management is using Azure Hybrid Worker server capabilities to trigger an installation of the updates. Please switch from Update Management Center to Update Management first and check all schedules in Update Management v1 (this is a part of Automation Account service)