Incorrect and impossible upload result using TCP

# Context

* Version of iperf3:
iPerf 3.1.3 (8 jun 2016 - 1.3 MiB for Windows Vista 64bits to Windows 10 64bits)

* Hardware:
Dell, CPU Intel i5-10310U @ 1.70GHz 16GB RAM, SSD disk and
Dell CPU Intel i5-5300U @ 2.30GHz 16GB RAM, SSD disk

* Operating system (and distribution, if any):
Windows 10 1909 Enterprise x64

# Bug Report

* Expected Behavior
Correct speed measurement

* Actual Behavior
Incorrect speed measurement

Look at this:
It's client. 5 Gbits/sec is impossible.

It's server in the same time.

I have now changed that the former client is now the server and the server is now the client. This is a screen from the client. Over 12 Gbit/s. Take a look at RAM.

These tests were performed on a local network on two of my computers. Ports on the network card are 1Gbps so as you can see these results are not correct.

I saw a similar problem when I was measuring to an external server outside my local network.

Could the problem be with some configuration of my operating system? Of course I don't use VPN, proxy etc., I closed other apps.
In the task manager, this speed is not visible in the network card graph and values.