We're running VUM 5.1.013071 on W2008R2 VM and vCenter Appliance 5.1.0.5100. Time to time I see a lot of queued "Check new notification" tasks. I must restart VMware vSphere Update Manager Service and enable VUM Extension plug-in. I can see "VMware vCenter Update Manager has restarted. The task was scheduled to run when Update Manager was not available and will run on the next scheduled time." errorr messages then.
I was able to "manually" download patches and upgrades before I've restarted VUM service. I've generated Update Manager log bundle before and after restart if it could help.
Thanks for an advice