VCSA: Unable to connect to server. Please try again.

Most likely you set the VCSA to regenerate its certificates upon reboot and forgot to uncheck it after the reboot. (It’s under Admin > Certificate Regeneration Enabled). So each time you reboot VCSA gets a new certificate and your browser throws the above error.

Fix is to refresh (Ctrl+F5 in Firefox) the page so the new certificate is fetched and you get a prompt about it.