Today I tried to open the Update Manager and got the following error.
Authentication failed, Update Manager server could not be contacted
When searching the VMware KB I found the following Article:
https://kb.vmware.com/s/article/60436
But I already had the mentioned Version installed.
A restart of the Update Manager Service or login/logoff on the HTML5 UI didn’t fixed the issue as described in:
https://communities.vmware.com/t5/Update-Manager-Discussions/VUM-failed-to-authenticate/m-p/2751225
At the end I was able to fix the issue by restarting the HTML5 UI Service as well with:
service-control --stop vsphere-ui;service-control --start vsphere-ui