Recently I upgraded my system from 11.3 U5 to 12.0 U1.1 directly.
Before upgrade, after I click the refresh button, it will select the default train.
After I upgraded to 12.0 U1.1, after I click the refresh button., system doesnt show any update train, but an error message: "Automatic update check failed. Please check system network settings."
I verified network is fine and our firewall passed traffic as well.
Also tested different browsers with private window as well, all got same result: