iperf: Question about high UDP packet loss (receiving) when bitrate increases

I am testing the occurrence of packet loss on a fiber network using iperf. As I increase the target bitrate from 10Mb/s to 500 Mb/s to 1000 Mb/s, I see increasingly high packet loss. This surprises me, as wouldn't expect a high packet loss on fiber network.

Question: Unless I am missing something about the network configuration, why would UDP packets be dropped at such a high rate between 500 Mb and 1000 Mb? Is it possible that there is a hardware issue preventing higher throughput?

# Target 10 Mb bit rate: % iperf3 -c 18.219.193.112 -u -b 10Mb -p 5201 -t 10 -i 2 Connecting to host 18.219.193.112, port 5201 #... [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams [ 5] 0.00-10.00 sec 11.9 MBytes 10.0 Mbits/sec 0.000 ms 0/8632 (0%) sender [ 5] 0.00-10.00 sec 11.9 MBytes 10.0 Mbits/sec 0.337 ms 0/8632 (0%) receiver # Target 500 Mb bit rate: % iperf3 -c 18.219.193.112 -u -b 500Mb -p 5201 -t 10 -i 2 Connecting to host 18.219.193.112, port 5201 #... - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams [ 5] 0.00-10.00 sec 596 MBytes 500 Mbits/sec 0.000 ms 0/431593 (0%) sender [ 5] 0.00-10.00 sec 496 MBytes 416 Mbits/sec 0.038 ms 71414/430453 (17%) receiver # Target 1Gb bit rate: % iperf3 -c 18.219.193.112 -u -b 1Gb -p 5201 -t 10 -i 2 Connecting to host 18.219.193.112, port 5201 [ 5] local 192.168.4.20 port 56530 connected to 18.219.193.112 port 5201 #... - - - - - - - - - - - - - - - - - - - - - - - - - [ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams [ 5] 0.00-10.00 sec 848 MBytes 712 Mbits/sec 0.000 ms 0/2553287 (0%) sender [ 5] 0.00-10.00 sec 580 MBytes 487 Mbits/sec 0.149 ms 2128163/2548332 (84%) receiver