I’d be interested in seeing the results from running ifstat with SMB (using fstab) and also UPnP.
To do so, take a look at this post. There will be no need to run with nohup, which allows the job to continue when you exit from the SSH session, so something like:
ifstat -nt -i eth0 >/home/osmc/smb.out 2>&1
ifstat -nt -i eth0 >/home/osmc/upnp.out 2>&1
will give us an idea of what’s happening on the network when using SMB and UPnP, respectively. Let each job run as long as you think necessary, then Ctrl-C to end it. Please upload the files produced to the OSMC pastebin using the command paste-log <filename>.