PCI Express x4 slot running at x1

The physical size of the PCIe connector on the motherboard denotes its configuration PCIe slots wired with Gen 2 or sometimes even Gen 1 slots In such cases

Try changing the bios settings for the slot you are using from what ever it is to GEN1

pcie 20 x1 slot PCIe adapters and bandwidth supported on the Power E850 Processor Modules Gen3 x16 and x8 slots All PCIe slots are hot-pluggable and enabled with

pcie x4 in x16 slot Socket Configuration ->VMD config for PStackN PCIE Slot Location Auto Gen1 Gen2 Gen3 Max Payload Size PCIE Max Payload Size Selection