Did you enable above 4g decoding in bios (if you have that option)
I cant see this option.
Flash the bios on your motherboard to 1.7 then it will be available.
Still cant find this after downgrade bios from 1.D to 1.7.
See this guide:
https://forum.z.cash/t/msi-z170-7-gpu-bios-setting-step-by-step/14473 (see Step 10, press F7 to enable advanced settings
)