WMS Upgrade from 4.1 to 4.3 -> JavaScript is disabled

I upgraded a customer's

console from 4.1 to 4.3 I know I need a free license now.

But regardless of which browser I try: IE, Firefox, Edge & Chrome, from different PCs and with and without incognito mode, I always get the HTML code which states: JavaScript is disabled!

I'm aware of the known issue in the PDF, but that doesn't help (Page 28): https://dl.dell.com/content/manual17061266-dell-wyse-management-suite-version-4-x-release-notes.pdf?language=en-us

How can I get those code to make my console work again?