After playing around for a few days in my lab with vCenter 6.7 I had to reboot my vCenter appliance. After reboot when I was trying connect back to HTML5 web client I received an error: 503 Service Unavailable (Failed to connect to endpoint: [N7Vmacore4Http16LocalServiceSpecE:0x00007fb6cc081b80] _serverNamespace = /ui action = Allow _port = 5090)