Unifi USW-Enterprise8 SFP+ to RJ45 transceiver performance issues one way traffic?

[Gio]

Hey folks; has anyone heard of Unifi issues with SFP+ to RJ45 transceivers where only one direction of traffic is impacted by performance issues?

I'm observing poor performance in what seems to be one direction of traffic.

My network setup
- USW-Enterprise8 with SFP+ to RJ45 to interconnect to US-XG-16
- USW-Enterprise8 has AP enterprise8 WIFI 6e ap for my home network
- US-XG-16 uses one of its RJ45 10G native ports to receive the uplink.
- 192.168.20.10 Synology NAS with 10GB port is connected to US-XG-16 10gb RJ45 port (I am seeing poor download speeds from the NAS when restoring backups; uploads are max speed which is why this issue remained in the shadows for long)
- "tower" Unraid NAS with 10GB SFP+ uplink to US-XG-16

Observations
- iperf3 in both directions ('-R' flag) between devices in same switch show full performance achieved.
- clients on WIFI 6e doing iperf to both unraid and synology - show very different performance characteristics. Not sure why, see below:

@mini ~ % iperf3-darwin -c tower.gfm -R
Connecting to host tower.gfm, port 5201
Reverse mode, remote host tower.gfm is sending
[  7] local 192.168.20.93 port 61074 connected to 192.168.20.28 port 5201
[ ID] Interval           Transfer     Bitrate         Rwnd
[  7]   0.00-1.00   sec  18.7 MBytes   157 Mbits/sec  1.99 MBytes                 
[  7]   1.00-2.00   sec  64.3 MBytes   539 Mbits/sec  4.00 MBytes                 
[  7]   2.00-3.00   sec   111 MBytes   933 Mbits/sec  4.00 MBytes                 
[  7]   3.00-4.00   sec   107 MBytes   900 Mbits/sec  4.00 MBytes                 
[  7]   4.00-5.00   sec   119 MBytes   998 Mbits/sec  4.00 MBytes                 
[  7]   5.00-6.00   sec   125 MBytes  1.05 Gbits/sec  4.00 MBytes                 
[  7]   6.00-7.00   sec   140 MBytes  1.17 Gbits/sec  3.78 MBytes                 
[  7]   7.00-8.00   sec   123 MBytes  1.03 Gbits/sec  3.96 MBytes                 
[  7]   8.00-9.00   sec   129 MBytes  1.08 Gbits/sec  4.00 MBytes                 
[  7]   9.00-10.00  sec   122 MBytes  1.03 Gbits/sec  4.00 MBytes                 
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  7]   0.00-10.01  sec  1.05 GBytes   898 Mbits/sec  528             sender
[  7]   0.00-10.00  sec  1.04 GBytes   890 Mbits/sec                  receiver

iperf Done.
@mini ~ % iperf3-darwin -c 192.168.20.10 -R
Connecting to host 192.168.20.10, port 5201
Reverse mode, remote host 192.168.20.10 is sending
[  5] local 192.168.20.93 port 61110 connected to 192.168.20.10 port 5201
[ ID] Interval           Transfer     Bitrate         Rwnd
[  5]   0.00-1.00   sec  13.1 MBytes   110 Mbits/sec   958 KBytes                 
[  5]   1.00-2.00   sec  26.4 MBytes   222 Mbits/sec   958 KBytes                 
[  5]   2.00-3.00   sec  22.6 MBytes   190 Mbits/sec   958 KBytes                 
[  5]   3.00-4.00   sec  25.0 MBytes   209 Mbits/sec   958 KBytes                 
[  5]   4.00-5.00   sec  20.7 MBytes   174 Mbits/sec   958 KBytes                 
[  5]   5.00-6.00   sec  18.8 MBytes   158 Mbits/sec   958 KBytes                 
[  5]   6.00-7.00   sec  17.9 MBytes   150 Mbits/sec   958 KBytes                 
[  5]   7.00-8.00   sec  27.5 MBytes   230 Mbits/sec   909 KBytes                 
[  5]   8.00-9.00   sec  29.0 MBytes   243 Mbits/sec   958 KBytes                 
[  5]   9.00-10.00  sec  25.6 MBytes   215 Mbits/sec   958 KBytes                 
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.02  sec   237 MBytes   198 Mbits/sec    0             sender
[  5]   0.00-10.00  sec   226 MBytes   190 Mbits/sec                  receiver

iperf Done.

Both NAS are sending me traffic from US-XG-16 to a wifi client/AP behind USW-Enterprise8. All devices are on the same vlan/broadcast domain so there is no router messing with this connection.

Any pointers on either what configuration problem I may have or explanation on why the native rj45 10GB port on the US-16-XG is behaving like this?