My

My snapshots have stopped working recently, and the following error with different .lock filenames appears in my WordPress' error log:

[13-Jun-2016 12:59:05 UTC] PHP Warning: fopen(/var/www/sites/production/wp-content/uploads/snapshots/_locks/1462809351.lock): failed to open stream: Permission denied in /var/www/sites/production/wp-content/plugins/snapshot/lib/Snapshot/Helper/Locker.php on line 25

The snapshots folder permissions are currently 777