Problems with TCP connection + loss

# Context

* Version of iperf3: 2.0.13

* Hardware: HP PAVILLON 15-n234sl

* Operating system (and distribution, if any): Ubuntu 20.04 on Virtualbox

Hi, I find myself using this tool of yours on a virtual machine with Ubuntu 20.04 installed. Since I was assigned the task of creating a topology with four hosts (h1 h2 h3 h4) where between h1-h3 there is a TCP connection while between h2-h4 a UDP connection. Between the central switches (s1 s2) there is a rate equal to 2 Mb, delay 10ms and Loss equal to 0% initially and then pass to 50%. However, although everything works fine at first and outputs the corresponding throughput, when I switch to the connection with 50% Loss, the TCP traffic generates me Throughput equal to 0. How can I do to solve?