Since with the new RX 500 series, you must have installed latest drivers to be able to run and mine correctly. But there is a problem, beside of Linux there is (was) no way to run more than five cards with one rig, the 6th or 7th card were not recognized at all because of some driver bug.
After many tests, someone tried a strange mix of drivers and for some reason it worked.
GrinI was able to get 6 x RX-500 series running on windows 10 x64. After two days the stupidest thing I tried worked.
So If you are struggling running 6 cards at once here is what you should do to fix it
How to get 6 RX 500 series GPUs to run together on Windows 10 for Mining Ethereum, Zcash, Monero etc..
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Once extracted both driver versions, go to extracted files of driver version 16.11.5 C:\AMD\WHQL-Win10-64Bit-Radeon-Software-Crimson-16.11.5-Sep13\Packages\Drivers\Display\WT6A_INF\B306709 and copy everything
Then go to driver version 17.5.1 C:\AMD\Non-WHQL-Win10-64Bit-Radeon-Software-Crimson-ReLive-17.5.1-May4\Packages\Drivers\Display\WT6A_INF\B313823 and paste the files that you just copied from 16.11.5