Symptoms:
You see messages in the vCenter Menu > Tasks > Recent Tasks similar to:
Task Name: "Check notifications"
Target: "vcenter-sddc-xx-xx-xx-xx.vmwarevmc.com"
Status: "? Queued"
Initiator: "VMware vSphere Update Manager Check Notification"
Example:
When navigating to vCenter Menu > Administration > Solutions > Client Plug-ins, you can see the vSphere Update Manager (VUM) plug-in State is "N/A", meaning the plug-in is disabled.
Example: