Plug-in View is missing in the vSphere Client

A specific view is missing in the vSphere Client.
Navigating to some extension point shows
Page Not Found
.
The view was not loaded by the vSphere Client.
Verify that the view URL is correctly defined in the plug-in manifest file.
Verify directly that the URL is reachable from the plug-in server, bypassing the vCenter Server reverse proxy.