I disabled xHCI in the BIOS and that may have fixed things... I thought that was needed for USB 3 ports, but they still work without xHCI.
About the Mamba.
I couldn't leave it alone. I thought: "New Year, new possibilities!"

I flashed it back to the 1.58 fw and the shut downs started again. Can't have that, so I flashed it back to the latest beta. But this time, I unhooked the "auto" tickmark in the Zbootloader. This time the flash stopped at "download successful!!!" and then I unplugged the stick and reconnected it again... Voilá! Now it works and the blue light is on!!!
