Error message starting ... and general sync failure

Nextcloud version: 13.0.5
Operating system and version: Debian 9
Apache or nginx version: Apache 2.4.25-3+deb9u5
PHP version: 7.0

The issue you are facing:
I am trying to sync my software development directory. Errors are coming up in red, such as:

...keys\/files\/development\/Clients\/Alliant\/com_users2528\/site\/models","models",3,3,"4102de576fe0c7ada5644f63ba136984"];

This gives the appearance that there may be more text to the left of the message, but I don’t see any way to look at it. I don’t know what the message means. There are also numerous errors in the log. After a while, nextcloud abandons the sync completely.

Is this the first time you’ve seen this error?: Y (but it’s also the first time I’ve tried to sync this directory)

Steps to replicate it:

  1. Try to sync my development directory

The output of your Nextcloud log in Admin > Logging:

Numerous instances of "OCP\Files\InvalidPathException:" at ...public_html/apps/dav/lib/Connector/Sabre/QuotaPlugin.php - line 210: OC\Files\View->free_space('development/Ali...')

Numerous instances of "OCP\Encryption\Exceptions\GenericEncryptionException: Bad Signature" at ...public_html/apps/encryption/lib/Crypto/Crypt.php - line 465

Numerous instances of "Sabre\DAV\Exception: An exception occurred while executing 'INSERT INTO `oc_filecache` (`mimepart`,`mimetype`,`mtime`,`size`,`etag`,`storage_mtime`,`permissions`,`parent`,`checksum`,`path_hash`,`path`,`name`,`storage`) SELECT ?,?,?,?,?,?,?,?,?,?,?,?,? FROM `oc_filecache` WHERE `storage` = ? AND `path_hash` = ? HAVING COUNT(*) = 0' with params ["1", "2", 1534065563, -1, "5b6ffb9bef877", 1534065563, 31, 186303, "", "15f11f65b8a2f9814d36e0e9fdcc31ad", "files_encryption\/keys\/files\/development\/Clients\/PERONii", "PERONii", 3, 3, "15f11f65b8a2f9814d36e0e9fdcc31ad"]: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '3-15f11f65b8a2f9814d36e0e9fdcc31ad' for key 'fs_storage_path_hash'" or similar

Numerous instances of "	OCA\DAV\Connector\Sabre\Exception\FileLocked: "development" is locked" with various files or directories.

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
  'instanceid' => 'ocdx0h2o6yoh',
  'passwordsalt' => '???',
  'secret' => '???',
  'trusted_domains' => 
  array (
    0 => 'cloud.example.com',
    1 => 'example.cloud',
  ),
  'datadirectory' => '/var/lib/nextcloud',
  'overwrite.cli.url' => 'https://cloud.example.com',
  'dbtype' => 'mysql',
  'version' => '13.0.5.2',
  'dbname' => 'nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'dbuser' => 'nextcloud',
  'dbpassword' => '???',
  'installed' => true,
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'maintenance' => false,
  'filelocking.enabled' => true,
  'memcache.locking' => '\\OC\\Memcache\\Redis',
  'redis' => 
  array (
    'host' => '/var/run/redis/redis.sock',
    'port' => 0,
    'timeout' => 0.0,
  ),
  'updater.secret' => '?????',
  'theme' => '',
  'loglevel' => 2,
);

The output of your Apache/nginx/system log in /var/log/____:

Nothing very interesting.