This message was posted on behalf of Intel Corporation
There are many reasons that affects speed performance. The first thing you can check is to use latest driver for your I219-V, You can try using Intel driver at https://downloadcenter.intel.com/product/82186/Intel-Ethernet-Connection-I219-V but we still recommend you to contact Gigabyte the board vendor for latest driver as they have customize driver that is compatible for their system.
Try change cable if there is spare one to see if this will make any difference.
You can try adjusting the advance setting on the adapter property by referring to the website below, please note not all setting are available as different NIC has their different advance setting:
Try to check your router or swtich setting as well if there is any optimization to be done on the router that could expedite the speed. Try to configure the NIC speed and duplex to be the same configuration on the switch.
Please contact Gigabyte for further support as well since onboard NIC are supported by system vendor, here is the website information regarding the scope of the support for Intel networking