Answer

The issue is caused by built-in Intel Wi-Fi driver in Windows 10 RS5(build 1809, 10.0.17763.1). Please set CPU core to less than 10 cores in BIOS before you install Windows 10 RS5. Please follow below procedures:
1. Enter BIOS menu, then go to Overclocking > Downcore Control.
2. Set "Downcore Control" as "ONE (1 + 0) 4 Cores" or "TWO (1 + 1) 8 Cores" or "TWO (2 + 0) 8 Cores", then save & exit BIOS.
3. Install Windows 10 RS5.
4. Install Wi-Fi driver with the MSI driver DVD or the Wifi driver downloaded from MSI website.
5. After Windows 10 RS5 and Intel Wi-Fi driver installation complete, Go to BIOS menu and set "Downcore Control" as Auto, then save & exit BIOS.
6. System should work properly now.