Guys, I registered here just to share my success with you. I have finally managed to make my MSI Z270  SLI PLUS motherboard to recognise all 8 graphics cards. Previously I struggled like some of you, updating BIOS, changing all the settings, trying various combinations but nothing helped to make cards recognised via M.2 risers. In the end it was as simple as using different make M.2 risers. I was successful with LATTCURE PCI-E 4X Female to NGFF M.2 M Key Male Adapter Power Cable with Converter Card (2 Packs) from amazon.co.uk
They are white colour scheme, with 2 LEDs (5V and 12V indicators).

I know how frustrating it must be when MSI advertise that this board can do 8 GPUs but won't explain how or recommend risers. I am happy to answer any questions and share screenshots. Just let me know what you want to see.

You should have just messaged me first and waited for a refund or another copy which is valid before posting this. It was as simple as that. People like you disgust me.