So, after successfully downloading a torrent, the Preview option is unavailable; it is greyed out even though the content is fully downloaded. In such a case, I can't find out how to play the download. Sometimes a download appears with "snapshots" becoming available early in the download, then the little green arrow appears under the Preview column and then the Preview button is available upon completion and all is well. At other times, downloads do not have either the snapshots or the green arrows showing during the download, and at the end, no Preview option is available.
How do I play such downloads, or know which downloads to avoid?