This doesn’t sound like a libNFS (Kodi built in NFS) issue to me, as you are having the problem both with Kodi’s libnfs and Kernel mounts - I see a pause of about a second randomly a few times during a TV episode if I use the Kodi built in NFS client however I do not have any issues if I use a kernel NFS mount. My NFS server is just the standard built (bsd) nfsd on a Mac Mini.
Can you post your exact fstab line (with IP’s changed if you prefer) including all the mount options you are using ?
This is mine for comparison, which is working perfectly for me on my Vero 2:
192.168.0.10:/Users/admin/Movies /mnt/Mac-Mini nfs noatime,noauto,x-systemd.automount,async,nfsvers=3,rsize=8192,wsize=8192,nolock,nofail,local_lock=all,soft,retrans=2,tcp 0 0
Also it would be very helpful if you would post (via the Log Uploader) a system journal and Kodi debug log taken after the issue manifests, and point out the exact time when the problem occurs.
Some additional thoughts - is flow control enabled on the switch the Vero is connected to ? (It is for me, but some switches default this to off)
Have you run an iperf test between the Vero and NFS server ? Remember that you need to run the iperf server on the Vero and the client on the NFS server to test receive speed at the Vero.
What bitrate are these rips ? Are they full blu-ray rips or are they at a lower bitrate ? Do you know roughly at what bitrate you start to have problems ? A good way to test is using the “jellyfish” clips, available here:
Download the 10,20,30,40,50,60 Mbps versions of these and put them on your server, then attempt to play them - find the fastest one that plays right through without pausing or buffering. I would recommend testing with the h264 versions.
You should be able to play up to about 80Mbps over the 100Mbps connection, which is more than enough for a full rate blu-ray rip which is typically 50Mbps max.
Finally, have you tried copying the offending file(s) to a USB stick or SD card and playing it while directly plugged into the Vero to see whether it is in fact a network issue ?