NVME M2 drives: which slot to use?

My M2_1 slot does not seem to be detecting my NVME SSDs, they work fine in the M2_2 slot Does anyone know why? I want to use both M2

Four NVMe SSD slots on a PCIe x16 card Silent operation Add your own SSDs up to 16TB Devotes four lanes of PCIe bandwidth to support full

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slot v cazinouri Hi, the board specification states: When installing devices in _2, PCI_E2 & PCI_E3 slots at the same time, PCI_E3 slot will be