I'm also having issues with my Z270-P

Specs:

ASUS Z270p
Intel Celeron G3900
8GB DDR4
8x EVGA 1070 SC Edition

BIOS Info:
[1] 4G Encoding: Enabled
[2] Primary Display: CPU Graphics
[3] DMI Max Link Speed: Gen 2
[4] PCIEX16_1 Link Speed: Gen 2
[5] PCIe Speed: Gen 2
[6] HD Audio Controller: Disabled
[7] M.2_1 Configuration: PCIE

I have been able to get 4 cards working, but when I plug in the 5th, I get the Splash Screen for a sec and then it fails to boot. I have tried:
1. Swapping to Gen 1's
2. Plugging in 5th -> Disabling 4G -> Reseting and failing to load Win -> Boot to BIOS -> Enable 4G -> Reset
3. Setting DMI Max Link Speed & PCIEX16_1 to "Auto" and PCIe Speed to Gen 1.

None of these worked. I'm beginning to think it might be a cable thing, but I tried every one of the 4 that aren't plugged in into the MoBo and they all have the same result? So I'm not sure. Any advice you can provide is appreciated.

Edit: I should say I can also get any 4 GPU's working in any combination.. But as soon as I add any 5th card in any slot it fails. I can also get to the BIOS fine, but as soon as it tries to boot Win10, it fails.