My 1st guess is that you have your Keep incomplete files option set to default which is 7 days. This is a common mistake. So go to LW's menu Tools>Options>Saving & change it from 7 days to 999. Press apply button.

The other thing that might have happened is your incomplete preferences have become corrupt due to LW not being closed down properly before shutting down the computer. This can happen if you shutdown too soon after closing LW or else, your computer crashed whilst LW was running.

You can highlight/select the files from the incomplete folder via the Library window & hit the Resume button. Unfortunately, they will probably start from 0%. But at least you can downld the files you were after.