How are you backing up your BDs? To ISO or MKV?
Mediainfo on one of the files may help: https://discourse.osmc.tv/t/mediainfo/
Logs while the problem is happening is always helpful: How to submit a useful support request - General - OSMC
To rule out the actual file, copying the file locally to the Vero is a good test.
Another good test is to use dd to copy the file as that’s a more real-life test than iperf3. On the Vero (from a ssh session)
dd if=/path/to/questionable/file.mkv of=/dev/null status=progress