Looks like one of the graphic cards is defective. However, I am looking internally and I will get back to you ASAP with a responce
Thanks, if it is a hardware problem then I have narrowed it down to 2 of the RX480s or their respective PCI-e risers. The hunt continues, but it is a bit of a slow process. Do you know if there are any test software for AMD cards on Linux? I am also a bit unsure what to tell the shop where I bought the card, I don't think 'This card will crash my machine if I run it continously doing crypto coin calculations, after 1-2 days, but it works fine as a "normal" graphics card.'