Why does above 4G decoding (when enabled) disable my ethernet (RTL8111H) on windows?

In Dortania's opencore guide for AMD Zen (17h) it says to enable above 4G decoding in the BIOS.

First of all I wanna know what it does and why does it disable my ethernet on windows?

I've not installed macOS yet to check what it does to my windows partition (yes i'm putting them on the same drive and if you can give advice with proof of what happens etc please do).