Go read this if not did before:

https://forum-en.msi.com/index.php?topic=288624.0

I also had problems with MSI z270 gaming m3.
It should support 4 GPUs but at fact it crashes when I start mining on 4.
I tried everything EVERYTHING, spent about 1 week to make it work but failed.
Then I just bought asus z270-p and everything works perfect from the box.

Gonna tell MSI they do shitty MBs.

Regards,
xkreed.