Symptoms:

• Specific vSphere Web Client with missing plug-ins when vCenters Servers are in Enhanced Linked Mode. For Example: Update manager plugin, SRM plugin, NSX plugin 

And

• vsphere_client_virgo.log reports:

com.vmware.vise.vim.extension.VcExtensionManager Package <plug-in Name> was not installed!
followed by 
Error downloading <plug-in download URL>

Location of vsphere_client_virgo.log:

• vCenter Server that runs on Windows: C:\ProgramData\VMware\vCenterServer\logs\vsphere-client\logs
• vCenter Server Appliance : /var/log/vmware/vsphere-client/logs

VMware vCenter Server Appliance 6.0.x
VMware vCenter Server Appliance 6.5.x
VMware vCenter Server 6.0.x
VMware vCenter Server 6.7.x
VMware vCenter Server Appliance 6.7.x
VMware vCenter Server 6.5.x

This situation occurs when the same plug-in extension is registered through multiple vCenters.
The extension manager of vSphere Web Client selects the first registration to download the package instead of downloading the same package multiple times. 
This would avoid potential package deployment problems from same plug in getting downloaded more than once.
In case the first vCenter plug-in URL selected is not reachable, it might result in missing plug-ins situation with vSphere Web Client.

Ensure network connectivity can be established from the impacted vCenter server to the plug-in download URL noticed in vsphere_client_virgo.log

Workaround:

Manually upload the package to impacted vSphere Web Client from another vCenter:

1. Stop vSphere Web Client service on the impacted vCenter Server
2. Take backup of vc-packages/cm-service-package folder in the vCenter with impacted vSphere Web Client

vc-packages folder location for the plug ins published to web client as vCenter Extensions:

vCenter Server that runs on Windows: C:\ProgramData\VMware\vCenterServer\cfg\vsphere-client\vc-packages
vCenter Server Appliance : /etc/vmware/vsphere-client/vc-packages

cm-service-package folder location for the plug-ins published as SSO service:
vCenter Server that runs on Windows: C:\ProgramData\VMware\vCenterServer\cfg\vsphere-client\cm-service-packages
vCenter Server Appliance : /etc/vmware/vsphere-client/cm-service-packages

3. Take the relevant  plug-in package folders from the vCenter where Plug-in is visible in vSphere Web Client and copy to impacted vCenter Server's vc-packages/cm-service-package folder 
4. Take the backup of work and pickup folder from the impacted vCenter Server and delete the contents of the pickup and work folder.

Note: copy the folders to some other location as backup and avoid renamed backup folders in the same location

pickup and work folder location:
     
     vCenter 6.0 that runs on Windows:
     C:\Program Files\VMware\vCenter Server\virgo\server\pickup 
     C:\Program Files\VMware\vCenter Server\WebClient\server\work
     vCenter Server Appliance 6.0:
    /usr/lib/vmware-virgo/server/pickup
    /usr/lib/vmware-vsphere-client/server/work
    
    vCenter 6.5 and 6.7 that runs on Windows:
    C:\programdata\VMware\vCenterServer\runtime\vsphere-client\server\work
    C:\programdata\VMware\vCenterServer\runtime\vsphere-client\server\pickup
    vCenter Server Appliance 6.5 and 6.7:
    /usr/lib/vmware-vsphere-client/server/pickup
   /usr/lib/vmware-vsphere-client/server/work
  

5. start the vSphere Web Client
6. Log in to the vSphere Web Client and check the plug-in availability 

If this issue persists, contact VMware Support and note this Article ID (57727) in the problem description. For more information, see How to Submit a Support Request.