Okay, I figured it out after searching into the Sabre/Connector/File.php error and finding this: https://github.com/nextcloud/server/issues/9001
https://doc.owncloud.com/server/10.3/admin_manual/configuration/files/big_file_upload_configuration.html#long-running-uploads
I added this to config.php:
'filelocking.ttl' => 36000,It solves a 3600 second timeout that occurs regarding locking.