Please check logs for transactional locking:
https://doc.owncloud.com/server/admin_manual/configuration/files/files_locking_transactional.html
This helps in cases where multiple clients are connected. While file is downloaded on another device, the file can’t be deleted. Should be unlocked normally after the operations finish. Problem might be maybe PHP timeouts that maybe kill the process before it’s unlocked again.
Does it cleanup the locks later? (1hr or so?)