Why does iperf3 hang in server mode?

Question

Computer networks

On the computer I run iperf3 -s
On the other I run iperf3 -c the address of the computer -P 28 When the threads are up to 30 everything is fine, it’s worth increasing more than 30, there is a breakdown and the server freezes (there is a breakdown and erratic movement in the command window) Somewhere there is a plug, where I don’t understand