M2_2 unrecognized on taichi x370

Take a look in the board manual:
M2_1 supports both M2-SATA and PCIe NVME
M2_2 only supports PCIe NVME

There is nothing unclear. It is like designed by AMD and Asrock.
More precise:
M2_1 supports both M2-SATA and PCIe NVME (4 PCIe 3.0 lanes directly connected to the CPU)
M2_2 only supports PCIe NVME (4 PCIe 2.0 lanes connected to the x370 chipset).

With 860 msata in M2_1 you will loose the fast PCIe NVME slot.
With NVME in M2_2 you only get half speed for your fast 960 evo (compared to M2_1). But it will work.

Look at my sig:
The very fast 960 PRO with the OS is using the fast M2_1, the 960 EVO the half speed M2_2 (compared to M2_1).
But it is ok, there is no slow feeling with it, just benchmark tools are telling lower speed.

But i would never use a M.2 MSATA SSD on a NVME PCIe port. It has just the same speed as with a real SATA port. The only advantage: You need no extra cables.