Intel® Ethernet Connection I219-V Unable to Reach Gigabit Speed

Intel® Ethernet Connection I219-V can reach more than 900Mbps in Safe Mode. However, speedtest.net shows less than 500Mbps when Windows* is running in its normal mode.

• Double-check if the established connection speed in the settings can reach 1Gbps. To confirm this, go to Network and Internet Settings. View your Network Properties and scroll down to Link speed (Receive/Transmit).
• Ensure that the Model/Access-point/Switch or device on the other side comes with full Gigabit support.
• Test the speed on another system to ensure that it is not an issue regarding cable, operating system, Internet, and hardware itself.
• Update the driver to latest version. If Intel® Ethernet Controller is embedded on Original Equipment Manufacturer (OEM) system, it's best to check with the manufacturer as the software drivers linked from Intel page are generic versions, and can be used for general purposes. To avoid any potential installation incompatibilities on OEM system, Intel recommends checking with the OEM and use the software provided via system manufacturer.
• Ensure that Speed & Duplex settings on Advanced tab property of the Intel Ethernet Controller is set to Auto Negotiation.
• Lower the value or turn off interrupt moderation as this is best for handling many small packets so the driver is more responsive to incoming and outgoing packets.
• Disable other I219-V features such as offloading, Energy Efficient Ethernet, and flow control.
• If the system comes with TurboLAN Cfos, disable the service called cFosSpeed System Service. Closing the program doesn't make any difference, as that service keeps running in the background.
• Run netsh int tcp set global autotuninglevel=normal on command prompt to check if the issue is bug related to Windows Auto Tuning