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Sorry to hear you’re facing problems 
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In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): 13.0.4
Operating system and version (eg, Ubuntu 17.04): Ubuntu 16.04 LTS
Apache or nginx version (eg, Apache 2.4.25): 2.4.18
PHP version (eg, 7.1): 7.0.30
The issue you are facing: I have noticed on my machine and with other family members that we are seeing issues with files not being removed properly when it comes to syncing. Let me give an example from today. I had a 16GB file that was syncing with Nextcloud and I had to reboot or do something that interruped the sync process. In the end I deleted the 16GB file BEFORE it was done syncing. Now, the local client keeps trying to sync this file that no longer exists. I have stopped syncing and restarted, but that made no difference, it keeps trying to sync this file. When I go to the web portal and sign in I can’t delete the file and it gives me an error. Eventually what I ended up doing was deleting the actual file from the Nextcloud server, which then let me remove it from the portal and it gave up syncing. I have never had this issue until recently, so I am wondering if 13.0.4 was the cause of it.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
Delete a file that is in progress of being synced, watch as Nextcloud doesn’t realize it doesn’t exist anymore.
The output of your Nextcloud log in Admin > Logging:
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => '',
'passwordsalt' => '',
'secret' => '',
'trusted_domains' =>
array (
0 => 'localhost',
),
'datadirectory' => '/var/www/nextcloudstorage',
'overwrite.cli.url' => 'http://localhost',
'dbtype' => 'mysql',
'version' => '13.0.4.0',
'dbname' => 'nextcloud',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => '',
'dbpassword' => '',
'logtimezone' => 'UTC',
'installed' => true,
'maintenance' => false,
'memcache.distributed' => '\\OC\\Memcache\\Redis',
'memcache.local' => '\\OC\\Memcache\\Redis',
'memcache.locking' => '\\OC\\Memcache\\Redis',
'redis' =>
array (
'host' => 'localhost',
'port' => 6379,
),
'theme' => '',
'loglevel' => 2,
'updater.secret' => '',
);
I kept getting ffile is locked problem when synching from Linux.