Webdav access issue

Nextcloud version (eg, 20.0.5): 21.03
Operating system and version (eg, Ubuntu 20.04): ubunto 20.04replace me
Apache or nginx version (eg, Apache 2.4.25): replace me
PHP version (eg, 7.4): 7.4

The issue you are facing:

usign an application onmy cell phone to save data to a folder on NC.

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:

Fatal	webdav	OC\DB\Exceptions\DbalException: An exception occurred while executing a query: SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction

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

<?php
$CONFIG = array (
  'instanceid' => 'oc9inbki1oos',
  'passwordsalt' => '/NkDEyueMQsSTl/AksXKAbuprd3wC8',
  'secret' => 'secret',
  'trusted_domains' =>
  array (
    0 => 'mydomaina',
  ),
  'datadirectory' => '/var/www/clients/client1/web13/web/data',
  'dbtype' => 'mysql',
  'version' => '21.0.3.1',
  'overwrite.cli.url' => 'https://mydomain',
  'dbname' => 'c1nextcloud',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'user',
  'dbpassword' => 'secret',
  'installed' => true,
  'default_phone_region' => 'CA',
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'app_install_overwrite' =>
  array (
    0 => 'joplin',
  ),
  'maintenance' => false,
  'has_rebuilt_cache' => true,
  'theme' => '',
  'loglevel' => 2,
  'updater.release.channel' => 'stable',
);

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

  GNU nano 4.8                                                                                       error.log                                                                                                 
[Wed Jul 28 00:00:32.155336 2021] [:error] [pid 371285] python_init: Python version mismatch, expected '2.7.17', found '2.7.18'.
[Wed Jul 28 00:00:32.161987 2021] [:error] [pid 371285] python_init: Python executable found ''.
[Wed Jul 28 00:00:32.162015 2021] [:error] [pid 371285] python_init: Python path being used '/lib/python2.7:/lib/python2.7/plat-x86_64-linux-gnu:/lib/python2.7/lib-tk:/lib/python2.7/lib-old:/lib/python2.7/l>
[Wed Jul 28 00:00:32.162049 2021] [:notice] [pid 371285] mod_python: Creating 8 session mutexes based on 150 max processes and 0 max threads.
[Wed Jul 28 00:00:32.162073 2021] [:notice] [pid 371285] mod_python: using mutex_directory /tmp
[Wed Jul 28 00:00:32.317779 2021] [mpm_prefork:notice] [pid 371285] AH00163: Apache/2.4.41 (Ubuntu) mod_fcgid/2.3.9 OpenSSL/1.1.1f mod_python/3.3.1 Python/2.7.18 mod_perl/2.0.11 Perl/v5.30.0 configured -- r>
[Wed Jul 28 00:00:32.317834 2021] [core:notice] [pid 371285] AH00094: Command line: '/usr/sbin/apache2'
[Wed Jul 28 00:00:32.317935 2021] [mpm_prefork:warn] [pid 371285] AH00167: long lost child came home! (pid 729232)
[Wed Jul 28 06:48:30.438241 2021] [php7:error] [pid 1154599] [client 45.146.164.110:53946] script '/var/www/html/index.php' not found or unable to stat
[Wed Jul 28 17:20:56.756167 2021] [negotiation:error] [pid 1242170] [client 118.26.36.169:48322] AH00687: Negotiation: discovered file(s) matching request: /var/www/ispconfig/index (None could be negotiated>
[Wed Jul 28 17:21:11.731444 2021] [negotiation:error] [pid 1242356] [client 118.26.36.169:56612] AH00687: Negotiation: discovered file(s) matching request: /var/www/ispconfig/index (None could be negotiated>