Have you tried updating the bios on this motherboard?
Yes! I am currently using 7A75v12 (
https://www.msi.com/Motherboard/support/Z270-GAMING-PLUS.html)
Does it have to be in a special latency value? It is set by default in 32b. Pcie gen 1 o 2? UEFI o Legacy?
I've tried many permutations, all the same problem.
I've been trying with 4 GPU.
With disabled above 4g memory, only 3 GPUS are detected in most cases (sometimes all of them are able to mine)