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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): Gentoo
Apache or nginx version (eg, Apache 2.4.25): Lighttpd-1.4.45
PHP version (eg, 7.1): 7.1.16
The issue you are facing:
I had a hardware issue in that the drive that hosted my Nextcloud database was suffering multiple read-write errors. I’ve replaced it and everything is mostly working as expected, but I have a few files that have this error:
The item is not synced because of previous errors: Error transferring /path/to/affected/file - server replied: Forbidden (Sabre\DAV\Exception\Forbidden)
As far as I can tell from testing, files newly placed into a synced folder are OK, these errors are for just a few files that were there at the time that the drive failure occurred. I’ve tried deleting and re-uploading some of the affected files, but this doesn’t work either.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
http://batman.gyptis.org/zerobin/?510521ee4e7e8e49#LCxly5QXEvLiE2PB5TPXlWuYEfcsFT5b7K5IeKbGW1k=
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => 'xxxx',
'passwordsalt' => 'xxxx',
'secret' => 'xxxx',
'trusted_domains' =>
array (
0 => 'xxxx',
),
'datadirectory' => '/mnt/vault/nextcloud/data',
'overwrite.cli.url' => 'https://xxxx/nextcloud',
'dbtype' => 'mysql',
'version' => '13.0.1.1',
'dbname' => 'NextcloudDB',
'dbhost' => 'localhost:3306',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => 'Nextcloud',
'dbpassword' => 'xxxx',
'installed' => true,
'memcache.local' => '\\OC\\Memcache\\APCu',
'loglevel' => 2,
'maintenance' => false,
);
The output of your Apache/nginx/system log in /var/log/____:
2018-05-14 03:10:01: (server.c.1534) logfiles cycled UID = 0 PID = 9935
2018-05-14 17:46:28: (server.c.1828) server stopped by UID = 0 PID = 19335
2018-05-14 17:47:29: (log.c.217) server started