Once I used iperf3 with 100 different udp streams/srcports to troubleshoot an issue, a small % of connections had >90% packet loss and this caused the connection pool of this service to fill up until it had only failed connections waiting to time out or going extremely slowly. ISP told me it was a broken linecard in a router, so packets were being dropped/corrupted on the backplane between the linecards.

Traceroute and mtr didn't use enough ports to show the issue clearly.

I used this to identify some intermittent loss in one direction from I think Kyrgyzstan to the UK, There was a claim that sometime flows were fine and sometimes they weren't. Problem was an ECMP in Pakistan or Iran which was using udp port numbers to balance the flow. Could consistently get 25% loss with certain numbers and not with others.