Very Impressive Setup.
Here is a link that offers some suggestions on how to fix the Error 43: How to Fix AMD Radeon Graphics Error 43 on Windows 10 | Driver Talent .
Be sure both RX480 cards are properly seated in the PCIe Slots. That may cause a Error 43 to occur.
But before you try the suggestions from the link, do this basic AMD installation procedure first and see if the error disappears:
Try this basic method of uninstalling and reinstalling AMD Drivers.
First download the correct Full AMD driver set from AMD Support for your Desktop: Desktop (03/26/2018)
Make sure your Windows 10 is fully updated via Windows Update (including Optionals).
Disconnect the Internet from your computer to prevent it from installing a different GPU Driver than the one you are installing.
Use Windows 10 Uninstall to uninstall all AMD Drivers and software. Then use DDU in safe mode to completely eliminate all traces of the old AMD drivers and software related to the GPU.
Delete C:\AMD Folder. This prevents New and Old AMD driver files from installing and corrupting the installation process.
After rebooting from DDU, Reinstall the new AMD Full set of drivers. If it installed correctly, again delete C:\AMD folder to save Hard Disk space and reconnect to the Internet.