NC: 18.0.4 running on Ubuntu 16.04 LTS; Apache 2.4.?; PHP 7.2;
Suddenly, I noticed that my mobile clients (Iphone picture upload) was giving me internal server errors. While checking the admin panel I saw the following error messages:
*** Your web server is not yet properly set up to allow file synchronization, because the WebDAV interface seems to be broken.**
*** Error occurred while checking server setup**
*** Error occurred while checking server setup**
*** Error occurred while checking server setup**
- Your web server is not properly set up to resolve “/.well-known/caldav”. Further information can be found in the documentation.
- Your web server is not properly set up to resolve “/.well-known/carddav”. Further information can be found in the documentation.
Is this the first time you’ve seen this error? (Y/N):
The bottom two are pending since quite a while. I have this NC installation since quite a while and have done multiple updates without any issues. But these errors came out of nowhere and I dont even know where to start 
The intersting part is that the sync to desktop clients seems to work although it shows some errors for few files (500 Internal Server Error).
I cant access the logging interface, clicking on the Apps interface gets me three error messages (An error occured during your request) but the page doesnst load.
config.php:
<?php
$CONFIG = array (
'instanceid' => 'XXXX',
'passwordsalt' => 'XXXXX,
'secret' => 'XXXXXX',
'trusted_domains' =>
array (
0 => 'localhost',
1 => 'XXXXXX',
2 => '192.168.178.22',
),
'datadirectory' => '/media/veracrypt1/nextcloud-data',
'overwrite.cli.url' => 'http://localhost/nextcloud',
'dbtype' => 'mysql',
'version' => '18.0.4.2',
'dbname' => 'nextcloud',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => 'nextcloud',
'dbpassword' => 'XXX',
'installed' => true,
'maintenance' => false,
'updater.secret' => 'xxxxx',
'theme' => '',
'loglevel' => 2,
'filelocking.enabled' => true,
'app_install_overwrite' =>
array (
0 => 'calendar',
),
);
Apache log:
[Mon Jun 08 07:35:02.214080 2020] [mpm_prefork:notice] [pid 980] AH00163: Apache/2.4.43 (Ubuntu) OpenSSL/1.1.1g configured -- resuming normal operations
[Mon Jun 08 07:35:02.214087 2020] [core:notice] [pid 980] AH00094: Command line: '/usr/sbin/apache2'
[Mon Jun 08 09:10:02.082576 2020] [php7:error] [pid 16818] [client 195.54.160.135:35782] script '/var/www/html/index.php' not found or unable to stat
[Mon Jun 08 09:48:10.399556 2020] [php7:error] [pid 16815] [client 89.247.201.105:65229] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:117\nStack trace:\n#0 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(117): PDOStatement->execute(NULL)\n#1 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(1054): Doctrine\\DBAL\\Driver\\PDOStatement->execute()\n#2 /var/www/nextcloud/lib/private/DB/Connection.php(220): Doctrine\\DBAL\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#3 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Query/QueryBuilder.php(203): OC\\DB\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#4 /var/www/nextcloud/lib/private/DB/QueryBuilder/QueryBuilder.php(215): Doctrine\\DBAL\\Query\\QueryBuilder->execute()\n#5 /var/www/nextcloud/lib/private/Lock/DBLockingProvider.php(316): OC\\DB\\QueryBuilder\\QueryBuilder->execute()\n#6 [internal function]: OC\\Lock\\DBLockingProvider->releaseAll in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php on line 106
[Mon Jun 08 14:29:09.275157 2020] [php7:error] [pid 16937] [client 89.247.201.105:53249] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:117\nStack trace:\n#0 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(117): PDOStatement->execute(NULL)\n#1 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(1054): Doctrine\\DBAL\\Driver\\PDOStatement->execute()\n#2 /var/www/nextcloud/lib/private/DB/Connection.php(220): Doctrine\\DBAL\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#3 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Query/QueryBuilder.php(203): OC\\DB\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#4 /var/www/nextcloud/lib/private/DB/QueryBuilder/QueryBuilder.php(215): Doctrine\\DBAL\\Query\\QueryBuilder->execute()\n#5 /var/www/nextcloud/lib/private/Lock/DBLockingProvider.php(316): OC\\DB\\QueryBuilder\\QueryBuilder->execute()\n#6 [internal function]: OC\\Lock\\DBLockingProvider->releaseAll in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php on line 106
[Mon Jun 08 14:29:09.277156 2020] [php7:error] [pid 19183] [client 89.247.201.105:53247] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:117\nStack trace:\n#0 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(117): PDOStatement->execute(NULL)\n#1 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(1054): Doctrine\\DBAL\\Driver\\PDOStatement->execute()\n#2 /var/www/nextcloud/lib/private/DB/Connection.php(220): Doctrine\\DBAL\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#3 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Query/QueryBuilder.php(203): OC\\DB\\Connection->executeUpdate('UPDATE `oc_file...', Array, Array)\n#4 /var/www/nextcloud/lib/private/DB/QueryBuilder/QueryBuilder.php(215): Doctrine\\DBAL\\Query\\QueryBuilder->execute()\n#5 /var/www/nextcloud/lib/private/Lock/DBLockingProvider.php(316): OC\\DB\\QueryBuilder\\QueryBuilder->execute()\n#6 [internal function]: OC\\Lock\\DBLockingProvider->releaseAll in /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Driver/AbstractMySQLDriver.php on line 106
[Tue Jun 09 07:35:01.598939 2020] [mpm_prefork:notice] [pid 980] AH00171: Graceful restart requested, doing restart
Any idea where to start? Really frustrating when out of a sudden a super stable NC install goes to shit 