Getting below error while login to vCenter.
Tried re-registering the VUM but still the error is re-occurring.
Have you changed the vCenters IP etc recently or has anything else changed?
There was an error connecting to VMware vSphere Update Manager - [x.x.x.x:443]. The request failed because of a connection failure. (Unable to connect to the remote server)
VMware Knowledge Base
You can re-register the VUM to vCenter server using the steps in article below