I'm also experiencing issues when downloading the OVA image.
It is difficult to determine if the issue is due to network, OS or NetApp Support site.
The issue was repropduced by other team members with Windows 10 / Windows 7 clients with Firefox & IE. Also reproduced when downloading from a Mac book.
The issue occurs with different OVA images - ONTAP 8.3.1, 9.0 & 9.1 were tested.
For OVA file with ~ 585 MB / 783 MB as reported from the NetApp Support page, the download of the OVA image is completed with a size ~ 412MB, with varying sizes ranging within the KB level ( i.e. 412,552 KB, 412,067 KB, 412,379 KB, 412,212 KB)
After the corrupted files above were downloaded, a reboot has helped the full file size to be downloaded correctly, but the issue re-occurred on another day.
Trying to download similar size patches and install binaries from other vendors does not show the same behaviour, which suggests it is something to do with the NetApp Support site.