We recently had issues with our ECP. It doesn’t seem to be exactly the same as you see. After working with TAC for a few weeks with limited success, we had to consort to installing a new ECP system and redo the entire configuration of it.
For us the setup webUI was working all along, but not the admin webUI, ie where you define what systems and clusters you have in the system. This was "fixed" be us setting up a new ECP VM and re-doing all the configuration. If this does not fix it for you there must be something on the computer or network where you connect as a brand new pure vanilla installation of the VM can't likely have the same issue that you had on the other one.
