This is a known issue affecting vSphere 6.5.
Workaround:
To work around this issue, edit the startup arguments of vsphere-ui service:
- Open the C:\ProgramData\VMware\vCenterServer\cfg\vmware-vmon\svcCfgfiles\vsphere-ui.json file using a text editor.
- Append this line in the StartCommandArgs section:
-Dos.name=Windows Server 2012
- Restart the vSphere Web Client services by running these commands:
C:\Program Files\VMware\vCenter Server\vmon\vmon-cli.exe --stop vsphere-ui
C:\Program Files\VMware\vCenter Server\vmon\vmon-cli.exe --start vsphere-ui