Undeleted temporary files

Step #2 of views_data_export_garbage_collect() function should indeed take care of deleting the temporary files. However, in cases where that delete fails for whatever reason, the file_usage entry is not removed from the database, but the views_data_export entry is. The file_delete() only removes the file_usage if the actual file delete was successful, even when the force parameter is true. The attached patch explicitly removes the file_usage before doing the delete. This will allow system_cron to attempt to delete the stuck expired temporary file without logging an error that it is in use by views_data_export. Additionally, make sure that views_data_export_cron runs prior to system_cron so this garbage collect happens before system_cron.

Version of the patch for PHP 7

Sorry for the lack of attention to your issue, please accept my apologies.

Drupal 7 is going to be end-of-life'd by the community in approximately 1 month. →

As such, I am closing all non-critical looking, non-PHP compatibility issues for Views Data Export to tidy up the issue queues and reduce the noise. You can read about this on #3492246: Close down Drupal 7 issues.

If you feel like this issue has been closed by mistake, please do comment about re-opening it.
If you feel like the ticket is still relevant for the 8.x-1.x version of the module, then please search for a duplicate issue first, and if there really isn't one (and you've looked properly) then change the version on the ticket and re-open.

Thanks to everyone involved in this issue: for reporting it, and moving it along, it is truly appreciated.
The Drupal community wouldn't be what it is today without your involvement and effort, so I'm sorry that we couldn't get this issue resolved. Hopefully we'll work together in a future issue though, and get that one resolved :)