Don't know your full configuration, but that lower M.2 slot shares bandwidth with the PCIE_X8_2 slot, in fact I
suspect that both M.2 slots might share that bandwidth. That PCIEX8_2 slot in turn shares bandwidth with the PCIE_X16/X8_1 slot. With a Ryzen cpu:
and with A-Series/Athlon cpu:
Because each M.2 NVME drive requires 4 lanes (PCIE_X4) then with two M.2 drives you are using X8 lanes. So I don't see how you can have two M.2 NVME drives unless you have a single GPU video card and with the PCIE_X8_2 slot unoccupied.
Does that help or is there a different problem?