It's difficult to support zero-downtime, graceful restarts in modern UDP application. Historically, UDP was designed for simple single-packet request/response protocols like DNS or NTP, where graceful ...
The iperf3 client fails at the beginning of the UDP transfer in reverse mode. The iperf3 client command (on the Android phone) is: iperf3 --forceflush -c x.x.x.x -V -p 5208 -u -t 15 -i 5 -fK -4 -b ...