10Gbps NIC throughput is low
Although you have 10Gbps network connection, you are getting low throughput. It is due to the use of incorrect PCIe slots to connect the 10Gbps NIC.
There are a total 4 types of PCIe slots: PCIe x1, PCIe x4, PCIe x8, PCIe x16 (Figure 1).
Connect the 10Gbps NIC in PCIe x4 if the NIC is only 1 x 10Gbps port and connect to PCIe x8 if there are 2 or more 10Gbps ports in the NIC.
The PCIe x1 slot has a speed limit of 4Gbits/s. So, the Network connection of 10 Gbps NIC will be very slow (~3.5Gbits/s).