I wonder, I might be on the wrong track but I'll ask anyway: Do you use the Resume button on your files? If yes do you do it to a large no. of files during a session? Doing so to many files can mean each file seaches out for immediate sources every few mins but in the meantime most will end up queueing for great lengths of time. (It can even affect LW's connection quality.) This can use a lot of LW's resources. If LW is busy with a large no. of files to count to the next resumption attempt, & possibly if you're also using other of LW's resources such as searching, using the media player, etc. then for LW to suddenly attempt to rescue back all those resources/energy needed to complete & verify a very large dwnld - there may be a bit of a clash. Just a thought!
There may also be problems with attempting to verify the file (b/c it is so large also) & LW may be struggling to keep a full connection to that host. What type of host were you dwnlding from?
Another thought is that the file is corrupt.