Harvey Those are partial downloads.
Ah, yes... I did know about those, but haven't used Chrome in quite a while. They were present in my /Downloads share for quite a while before I closed Chrome. I suspect that most of the download activity stopped when word of the new version reached the main body of Solus fans.
I''m now assuming that the files generated by processing the torrents will be fine.
I'm testing that theory now, downloading them again using Firefox on a different computer. More Solus users are apparently awake by now, because the downloads are very slow. I'll let you know what I find out when one of them is finished.
It's just a guess, but I think Vivaldi (and other Chromium derivatives?) might be writing directly to the /Downloads/Linux/ share on my NAS, whereas Chrome might be buffering the downloads in these partial files, and writing them to the NAS when the downloads are finished. That buffering might be the difference in their speeds.