most probably, ask the service provider
Disable file locking in Nextcloud config file
One way to fix the file is locked error is to disable the file locking feature in Nextcloud. This feature is meant to prevent concurrent access and conflicts on files, but it can also cause problems if the locks are not released properly. To disable file locking, you need to edit the Nextcloud config file.
- edit config.php line that says
'filelocking.enabled' => true,and change it to'filelocking.enabled' => false,
This will disable the file locking feature in Nextcloud and you should be able to edit or delete your files without any error.
see also How to fix: File is locked error?