My apologies to all in this thread. The internal ethernet connection seems to work fine for me now.
I experimented with it last night, for what must have been the first time in nearly two years, after discovering subpar iPerf3 results for my Anker USB gigabit adapter:
iperf3 -R -t 60 -c 192.168.1.2
ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-60.01 sec 702 MBytes 98.1 Mbits/sec 491 sender
[ 4] 0.00-60.01 sec 700 MBytes 97.8 Mbits/sec receiver
Note the sub 100Mbps speeds and number of retries. Both of which were consistent across multiple tests. The same ethernet connection gives gigabit speeds and no retries on a MacBook Pro. No idea why the USB adapter is not resulting in a boost over 100Mbps anymore (I’m sure I tested this in the past), but I figured I might as well try the built-in ethernet again.
The built-in ethernet resulted in near-100Mbps speed (as expected) but 0 retries:
iperf3 -R -t 60 -c 192.168.1.2
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-60.00 sec 676 MBytes 94.5 Mbits/sec 0 sender
[ 4] 0.00-60.00 sec 674 MBytes 94.2 Mbits/sec receiver
I then tried playing a range of my 1:1 UHD rips using the built-in ethernet, and they all started fine without the buffering message I used to see. I couldn’t find a single one that triggered it. Also, I was able to skip forwards and backwards without issue. And even better; playing them via the Plex add-on (i.e. not from an NFS mount) worked absolutely fine too.
Something I need to clear up: I realised last night I had never actually tried the built-in ethernet since changing my network/NAS setup from Synology NAS + AirPort Extreme routers -> SSD Ubuntu NUC NAS + Synology routers. Many apologies - I had incorrectly implied above I had seen these issues in the current setup too.
So it seems that either software updates on the Vero, or my change in Network/NAS have significantly improved things for me, such that I’ll be using the built-in ethernet from now on.
I may still try some NFS tweaks - thanks @Theetjuh - but it no longer seems necessary.