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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): 13.0.1
Operating system and version (eg, Ubuntu 17.04):
Apache or nginx version (eg, Apache 2.4.25):
PHP version (eg, 7.1):
The issue you are facing:
Hello everybody,
I have nextcloud running on a Qnap NAS. As far as everything worked, since today I am, however, a mistake in the Syncronisation a file displayed. Nextcloud is configured on my smartphone so that all images are automatically uploaded via Wi-Fi. This error seems to have occurred. Unfortunately, I can not find the file in the file system at all. On the smartphone it is shown, however, defective and as soon as I want to delete it appears at the next update just on …
Is this the first time you’ve seen this error? (Y/N): YES
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
PASTE HERE
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
PASTE HERE
The output of your Apache/nginx/system log in /var/log/____:
PASTE HERE