I am not sure if this is a LW bug or something to do with partly fake download files. Check to see how many copies you have of that file in your incomplete folder.

I am aware that LW does sometimes stop with one incomplete then starts a new one. It has done this ever since LW version 2.

The fact many have reported this however suggests either a new bug else, a new type of spammed file to try to stop people downloading copyright files. I haven't had this problem yet but I'm using LW 4.16 at present. The latest LW version is 4.18.6 which 'might' have dealt with this issue. Unfortunately their history page has not been updated so I can not tell you.