Lol
I tested Z270-A PRO MSI and i had up and running 6 gpus.
Now i can run only 5

I messed with options.
Anybody have this motherboard and can tell what did you changed to work 6 gpus ?

Enable 4G Decoding & set PCIe to x1

Did it help? I have 4 pieces in the basket in the eshop and I hesitate to order it.
They are wrking fine !.
After alll i changes ALL risers and now its working with 6 gpus

So riser it was a fault !