Due to a change in my home network, I had to change the home lab to a different subnet.
It was no problem doing so for the hosts, switch, and storage, but I did notice that my vCenter Events window started filling up with VMware Update Manger (VUM) update notification errors.
Also, the VUM Plugin failed to enable in my vSphere Client?!?
After verifying again that I finished changing ALL management IPs, I was a little confused. So, I accessed the Encyclopedia of VMware Knowledge (aka VMware Communities), and I found many people with similar problems.
Suggested resolutions ranged from re-install VUM to re-install vCenter from scratch?!?
I figured there had to be a better way, and my diligence was rewarded when I found this article: Enabling the VMware vCenter Update Manager plugin generates errors
The suggestions in this article solved my problem. Updating the vci-integrity.xml and restarting the VUM-related Windows Services fixed the errors and allowed me to use the Update Manager Plugin in my vSphere Client.