Server is unreachable, it may be down or there is some problem with the network connection. You will be notified once the server is available.

As a part of the upgrade, the VIOM services are restarted thereby causing the VIOM session to expire.
Allow some time for the VIOM services to refresh the UI. Then, use the original URL to login back into the console.
e.g.
https://gpk730r4c-22.xxxxx.xxxxx.com:14161/
and login should proceed fine:
Server is unreachable after installing 7.4.0.600 patch