Unfortunately, regular downloads are subject to errors on larger assets for some reason. In T:ANE, it would complete the download but then complain that it lost connection. Well, yes it lost connection because the download was done! But if you right-clicked the asset and chose Download again, it would just see it and complete the install. Unfortunately, with TRS19 (and maybe 22? I don't know), something changed, so now the first part is the same, but as you observed, it gets almost done and starts over (gah!). Or, it will finish with the same error as T:ANE, but when you right-click it to start over it will start from scratch.
I believe there is some sort of bug in completing downloads that N3V has never fixed and everyone just wants us to buy FCTs, which I do occasionally, when I have some routes, sessions, or other things that call for multiple large downloads. For $6 USD you get a 30-day and you can do a WHOLE LOT of downloads in that 30 days!