They would be my first suspect when debugging network problems.
I see that you provided partial iperf figures above. Could you please repeat them and:
-R flag).Hi, is this what you needed? Ta
[ 5] local 192.168.0.10 port 41891 connected with 192.168.0.12 port 5001
[ ID] Interval Transfer Bandwidth
[ 5] 0.0- 0.0 sec 65.0 KBytes 190 Mbits/sec
Not exactly. I was hoping to see the full iperf (preferably iperf3) results both ways, together with the commands you ran. For example: Very weak WiFi performance
Ok, this better? 
admin@SynologyNAS:/$ iperf3 -s
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Accepted connection from 192.168.0.10, port 43950
[ 5] local 192.168.0.12 port 5201 connected to 192.168.0.10 port 43951
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.01 sec 6.42 MBytes 53.5 Mbits/sec 0 48.1 KBytes
[ 5] 1.01-2.01 sec 7.98 MBytes 66.9 Mbits/sec 0 62.2 KBytes
[ 5] 2.01-3.01 sec 8.70 MBytes 73.0 Mbits/sec 0 73.5 KBytes
[ 5] 3.01-4.00 sec 9.25 MBytes 78.0 Mbits/sec 0 83.4 KBytes
[ 5] 4.00-5.01 sec 9.88 MBytes 82.5 Mbits/sec 0 100 KBytes
[ 5] 5.01-6.01 sec 10.6 MBytes 89.0 Mbits/sec 0 150 KBytes
[ 5] 6.01-7.01 sec 11.2 MBytes 93.8 Mbits/sec 0 222 KBytes
[ 5] 7.01-8.00 sec 11.6 MBytes 97.9 Mbits/sec 0 315 KBytes
[ 5] 8.00-9.00 sec 10.9 MBytes 91.2 Mbits/sec 9 260 KBytes
[ 5] 9.00-10.00 sec 10.9 MBytes 91.9 Mbits/sec 0 294 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 97.5 MBytes 81.7 Mbits/sec 9 sender
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
osmc@htpc:~$ iperf3 -c 192.168.0.12 -R
Connecting to host 192.168.0.12, port 5201
Reverse mode, remote host 192.168.0.12 is sending
[ 4] local 192.168.0.10 port 43951 connected to 192.168.0.12 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 6.31 MBytes 52.9 Mbits/sec
[ 4] 1.00-2.00 sec 7.89 MBytes 66.2 Mbits/sec
[ 4] 2.00-3.00 sec 8.71 MBytes 73.1 Mbits/sec
[ 4] 3.00-4.00 sec 9.17 MBytes 77.0 Mbits/sec
[ 4] 4.00-5.00 sec 9.93 MBytes 83.3 Mbits/sec
[ 4] 5.00-6.00 sec 10.4 MBytes 87.6 Mbits/sec
[ 4] 6.00-7.00 sec 11.2 MBytes 93.6 Mbits/sec
[ 4] 7.00-8.00 sec 11.2 MBytes 94.0 Mbits/sec
[ 4] 8.00-9.00 sec 10.8 MBytes 90.9 Mbits/sec
[ 4] 9.00-10.00 sec 11.2 MBytes 93.8 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 97.5 MBytes 81.8 Mbits/sec 9 sender
[ 4] 0.00-10.00 sec 97.1 MBytes 81.4 Mbits/sec receiverYes, better. (I reformatted it so it’s now even better. 
)
The figures are a bit erratic but not that bad. I came to this thread a bit late, so missed one important point. In your first post you stated:
I assume you mean that you were copying files from the Vero4K+. The thing is that nothing in the log indicates that you’ve NFS-mounted the Syno NAS on the V4K+. So how exactly did you copy the files across?
Yep. Thanks for doing that - how did you do it btw?
I was copying from the Vero as you mentioned, just using Kodi’s file manager.
Highlight the text then click on the </> symbol.
TBH, I’ve never used the Kodi file manager over a Kodi NFS mount. You can run a small test that uses kernel-based NFS to see how it performs.
sudo mkdir /mnt/syno
sudo mount.nfs 192.168.0.12:/volume1/downloads /mnt/syno
then we can time the copy of a file:
time cp <filename> /mnt/syno
Cheers. Think I am just going to pop the drive in a caddy as the the simplest of solutions. Thanks for the assistance though.