MSI's forum support considers mining an illicit activity, they won't provide any support. (and their answers are often outright false)

Here's what your motherboard's manual says:

2x PCIe 3.0 x16 slots (supports x16/x4 mode)*
4x PCIe 3.0 x1 slots**
* The PCI_E4 slot will be unavailable when an M.2 SSD module has been
installed in the M.2_2 slot.
** The PCI_E2 slot will be unavailable when an expansion card has been
installed in the PCI_E5 slot.
** The PCI_E3 slot will be unavailable when an expansion card has been
installed in the PCI_E6 slot.

So, the PCI-E x1 slots use shared lanes and you can only use two in total, and if you use a m2 SSD it disables the second full length slot.
Getting four cards running should be possible using both full-length PCI-E x16 slots and then any two of the x1 slots.