Mate if he sold you a flashed card with mining BIOS this need to be fixed. I can guide you even on skype/raidcall step by step.
That is why asked you to post your BIOS versioning from ATIFlash and GPUZ here. (both BIOS)
Is easy to fix the card if needed.
Also is the reference one, not Red Devil as I thought so that is easy to even flash the Liquid BIOS to it
Also you bought a second hand £400 when there is already 2 weeks now the Red Devil offer

And please find the stickers on the PCB to confirm is Vega 64 not flashed Vega 56.
@Schizo I know you were involved a lot on that sale
https://forums.overclockers.co.uk/threads/powercolor-rx-vega-64.18827106/#post-32036247
and saw you had complains about the seller. What is your advice?