[6.10.0-rc2] Slow Upload speed via SMB/FTP, yet Download is fine

I've been encountering some weird performance issues with 6.10.0-rc2.

I'm using 1 Gbit/s connections both with my Unraid server and my Desktop PC.

This is what it looks like transfering a file from my Kingston A2000 in my Unraid server to my Desktop PC (this is via FTP; the same goes for SMB):

This is what it looks like transfering a file from my Desktop PC to my Unraid server via FTP (the same goes for SMB):

This is almost 3x faster, which should not be the case given that it's a working 1 Gbit/s connection to my router and going from my router to my Desktop PC.

And just for comparison's sake, this is an iperf3 test with my PC running as a server:

root@Tower:~# iperf3 -c 192.168.188.23 -u -p 5201 -b 1200m
Connecting to host 192.168.188.23, port 5201
[  5] local 192.168.188.24 port 37706 connected to 192.168.188.23 port 5201
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec   101 MBytes   843 Mbits/sec  72198
[  5]   1.00-2.00   sec  99.8 MBytes   837 Mbits/sec  71662
[  5]   2.00-3.00   sec  99.2 MBytes   832 Mbits/sec  71234
[  5]   3.00-4.00   sec  87.9 MBytes   738 Mbits/sec  63157
[  5]   4.00-5.00   sec  85.7 MBytes   719 Mbits/sec  61560
[  5]   5.00-6.00   sec  87.2 MBytes   732 Mbits/sec  62639
[  5]   6.00-7.00   sec  88.1 MBytes   739 Mbits/sec  63255
[  5]   7.00-8.00   sec  85.4 MBytes   717 Mbits/sec  61368
[  5]   8.00-9.00   sec  87.2 MBytes   732 Mbits/sec  62651
[  5]   9.00-10.00  sec  86.0 MBytes   721 Mbits/sec  61754
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec   907 MBytes   761 Mbits/sec  0.000 ms  0/651478 (0%)  sender
[  5]   0.00-10.00  sec   456 MBytes   383 Mbits/sec  0.052 ms  323474/651235 (50%)  receiver

iperf Done.
root@Tower:~# iperf3 -c 192.168.188.23 -u -p 5201 -b 1200m -R
Connecting to host 192.168.188.23, port 5201
Reverse mode, remote host 192.168.188.23 is sending
[  5] local 192.168.188.24 port 45272 connected to 192.168.188.23 port 5201
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-1.00   sec  35.8 MBytes   300 Mbits/sec  0.059 ms  0/25697 (0%)
[  5]   1.00-2.00   sec  40.3 MBytes   338 Mbits/sec  0.023 ms  0/28916 (0%)
[  5]   2.00-3.00   sec  40.5 MBytes   340 Mbits/sec  0.023 ms  0/29101 (0%)
[  5]   3.00-4.00   sec  40.8 MBytes   342 Mbits/sec  0.023 ms  0/29315 (0%)
[  5]   4.00-5.00   sec  39.8 MBytes   334 Mbits/sec  0.023 ms  0/28560 (0%)
[  5]   5.00-6.00   sec  40.3 MBytes   338 Mbits/sec  0.026 ms  0/28945 (0%)
[  5]   6.00-7.00   sec  40.5 MBytes   340 Mbits/sec  0.025 ms  0/29082 (0%)
[  5]   7.00-8.00   sec  40.7 MBytes   341 Mbits/sec  0.026 ms  0/29226 (0%)
[  5]   8.00-9.00   sec  40.7 MBytes   341 Mbits/sec  0.025 ms  0/29221 (0%)
[  5]   9.00-10.00  sec  40.6 MBytes   340 Mbits/sec  0.024 ms  0/29130 (0%)
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Jitter    Lost/Total Datagrams
[  5]   0.00-10.00  sec   400 MBytes   335 Mbits/sec  0.000 ms  0/287193 (0%)  sender
[  5]   0.00-10.00  sec   400 MBytes   335 Mbits/sec  0.024 ms  0/287193 (0%)  receiver

iperf Done.
root@Tower:~#

And vice-versa with my Unraid server running as a server:

D:\Programme\iperf3>iperf3 -c 192.168.188.24 -u -p 5201 -b 1200m
Connecting to host 192.168.188.24, port 5201
[  4] local 192.168.188.23 port 50135 connected to 192.168.188.24 port 5201
[ ID] Interval           Transfer     Bandwidth       Total Datagrams
[  4]   0.00-1.00   sec  99.1 MBytes   831 Mbits/sec  12688
[  4]   1.00-2.00   sec   110 MBytes   923 Mbits/sec  14083
[  4]   2.00-3.00   sec   110 MBytes   922 Mbits/sec  14073
[  4]   3.00-4.00   sec   110 MBytes   919 Mbits/sec  14021
[  4]   4.00-5.00   sec   107 MBytes   898 Mbits/sec  13699
[  4]   5.00-6.00   sec   110 MBytes   923 Mbits/sec  14087
[  4]   6.00-7.00   sec   110 MBytes   923 Mbits/sec  14089
[  4]   7.00-8.00   sec   109 MBytes   916 Mbits/sec  13976
[  4]   8.00-9.00   sec   110 MBytes   920 Mbits/sec  14035
[  4]   9.00-10.00  sec   109 MBytes   913 Mbits/sec  13927
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
[  4]   0.00-10.00  sec  1.06 GBytes   909 Mbits/sec  0.588 ms  5703/5954 (96%)
[  4] Sent 5954 datagrams

iperf Done.

D:\Programme\iperf3>iperf3 -c 192.168.188.24 -u -p 5201 -b 1200m -R
Connecting to host 192.168.188.24, port 5201
Reverse mode, remote host 192.168.188.24 is sending
[  4] local 192.168.188.23 port 54257 connected to 192.168.188.24 port 5201
[ ID] Interval           Transfer     Bandwidth       Jitter    Lost/Total Datagrams
[  4]   0.00-1.00   sec  8.00 KBytes  65.5 Kbits/sec  102269683364.602 ms  0/1 (0%)
[  4]   1.00-2.00   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   2.00-3.01   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   3.01-4.01   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   4.01-5.01   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   5.01-6.01   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   6.01-7.00   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   7.00-8.00   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
[  4]   8.00-9.01   sec  0.00 Bytes  0.00 bits/sec  102269683364.602 ms  0/0 (0%)
iperf3: error - unable to receive control message: Connection reset by peer

Something is clearly not working properly here, but I can't figure out what. This is a fresh install with just a couple of settings changed (like creating an FTP User and an SMB User) in addition to reinstalling my Docker containers. For this test though, Docker has been completely disabled.

I've attached a diagnostics file; maybe somebody can figure out what's going on.

tower-diagnostics-20211108-2210.zip