I've always had better luck with gen 1.
You can try the standard stuff
-Make sure crossfire is disabled
-Turn HBCC off
-Reinstall drivers
Honestly, on my two vega rigs occasionally they won't see the 4th card. I just restart until they do. 2-3 restarts generally fixes it for me.
You may have better luck posting your question in the main vega thread. If you haven't read through it already, it really does have some good stuff in there:
https://bitcointalksearch.org/topic/any-word-on-amd-vega-hash-rates-2002025
Topic: 4th Vega 0xc00000bb initialize failure Asrock h170a-x1 (Read 167 times)
No one? 
Hi,
just when the fourth card is active doesn't boot sometimes, after several restart it boot but windows only see 3 vega.
Set manual pcie to Gen2 but no change. There seems there isn't a 4G option.
In summer, with 4 1070 no Problems with booting and recognizing and mining with 4 gpu's.
Thanks for helping
just when the fourth card is active doesn't boot sometimes, after several restart it boot but windows only see 3 vega.
Set manual pcie to Gen2 but no change. There seems there isn't a 4G option.
In summer, with 4 1070 no Problems with booting and recognizing and mining with 4 gpu's.
Thanks for helping
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