Hey guys,
funny things happening with my new rig and I just cant get the hang of it.

So first of all here the specs:

Mobo: ASRock H81 Pro BTC R2.0 Intel H81 So.1150 Dual Channel DDR3 ATX Retail
CPU: Intel Pentium G3260 2x 3.30GHz So.1150 BOX
RAM: 4GB G.Skill Value DDR3-1600 DIMM CL11 Single
GPU: 4x Sapphire Radeon RX 560 Pulse 4GD5 Aktiv PCIe 3.0 x16 (Retail)
PSU:   850 Watt be quiet! Power Zone Modular 80+ Bronze
HDD: HGST 7ZK500
OS: Win10
Riser: all active risers with active power supply

Okay getting started, after booting up the OS I can start the tweaking tool for my cards and it won't show me more than three gpus, looking into the device manager one of them is shown with error code 12 - not enough ressources available.
When I start to mine I'll just get the three GPUs shown working.
Then I thought well maybe the PSU doesn't feature enough power so just lets take one GPU out and test the thing again.
Now it shows three GPUs in the decive manager but one with error code 12.
Same goes for the miner.

I've already switched tried out different ports, different raisers, different cards it just doesnt work.

So it doesnt matter how many GPUs I add to the rig, there is always one which gets the error code 12.
And it is not always the same PCI slot which is shown sometimes it is PCI2 sometimes it is PCI3 - pretty random actually.

Any ideas?