It seems the ASMedia* controller shares bandwidth among the PCI Express x16, USB 3.0, and SATA Express ports. You may want to check if other devices are connected to such ports and the related BIOS settings.
*1 : The PCIe x16_3, USB3_E56 and SATAExpress_E1 connectors share the same bandwidth. The PCIe x16_3's default setting is in Auto mode that automically optimizes the system bandwidth. If you use two of these connectors, the system automatically disables the unused connector.
DC P3600 plugged on PCIe slot from CPU not form PCH.