Fehler im Dashboard - "unbekannte Erweiterungen" und "Fehler beim Überprüfen der Overrides"

Es ist ein Fehler aufgetreten.
0 Attempt to assign property "element" on null
Call Stack
#    Function    Location
1    ()    JROOT/libraries/src/Updater/Adapter/ExtensionAdapter.php:73
2    Joomla\CMS\Updater\Adapter\ExtensionAdapter->_startElement()     
3    xml_parse()    JROOT/libraries/src/Updater/Adapter/ExtensionAdapter.php:287
4    Joomla\CMS\Updater\Adapter\ExtensionAdapter->findUpdate()    JROOT/libraries/src/Updater/Updater.php:264
5    Joomla\CMS\Updater\Updater->getUpdateObjectsForSite()    JROOT/libraries/src/Updater/Updater.php:165
6    Joomla\CMS\Updater\Updater->findUpdates()    JROOT/administrator/components/com_installer/src/Model/UpdateModel.php:276
7    Joomla\Component\Installer\Administrator\Model\UpdateModel->findUpdates()    JROOT/administrator/components/com_installer/src/Controller/UpdateController.php:113
8    Joomla\Component\Installer\Administrator\Controller\UpdateController->find()    JROOT/libraries/src/MVC/Controller/BaseController.php:730
9    Joomla\CMS\MVC\Controller\BaseController->execute()    JROOT/libraries/src/Dispatcher/ComponentDispatcher.php:143
10    Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()    JROOT/libraries/src/Component/ComponentHelper.php:361
11    Joomla\CMS\Component\ComponentHelper::renderComponent()    JROOT/libraries/src/Application/AdministratorApplication.php:150
12    Joomla\CMS\Application\AdministratorApplication->dispatch()    JROOT/libraries/src/Application/AdministratorApplication.php:195
13    Joomla\CMS\Application\AdministratorApplication->doExecute()    JROOT/libraries/src/Application/CMSApplication.php:306
14    Joomla\CMS\Application\CMSApplication->execute()    JROOT/administrator/includes/app.php:58
15    require_once()    JROOT/administrator/index.php:32

##
# @package    Joomla
# @copyright  Copyright (C) 2005 - 2020 Open Source Matters. All rights reserved.
# @license    GNU General Public License version 2 or later; see LICENSE.txt
##

##
# READ THIS COMPLETELY IF YOU CHOOSE TO USE THIS FILE!
#
# The line 'Options +FollowSymLinks' may cause problems with some server configurations.
# It is required for the use of Apache mod_rewrite, but it may have already been set by
# your server administrator in a way that disallows changing it in this .htaccess file.
# If using it causes your site to produce an error, comment it out (add # to the
# beginning of the line), reload your site in your browser and test your sef urls. If
# they work, then it has been set by your server administrator and you do not need to
# set it here.
##

## No directory listings
<IfModule mod_autoindex.c>
  IndexIgnore *
</IfModule>

## Suppress mime type detection in browsers for unknown types
<IfModule mod_headers.c>
Header always set X-Content-Type-Options "nosniff"
</IfModule>

## Can be commented out if causes errors, see notes above.
Options +FollowSymlinks
Options -Indexes

## Disable inline JavaScript when directly opening SVG files or embedding them with the object-tag
<FilesMatch "\.svg$">
  <IfModule mod_headers.c>
    Header always set Content-Security-Policy "script-src 'none'"
  </IfModule>
</FilesMatch>

## Mod_rewrite in use.

RewriteEngine On

## Begin - Rewrite rules to block out some common exploits.
# If you experience problems on your site then comment out the operations listed
# below by adding a # to the beginning of the line.
# This attempts to block the most common type of exploit `attempts` on Joomla!
#
# Block any script trying to base64_encode data within the URL.
RewriteCond %{QUERY_STRING} base64_encode[^(]*\([^)]*\) [OR]
# Block any script that includes a <script> tag in URL.
RewriteCond %{QUERY_STRING} (<|%3C)([^s]*s)+cript.*(>|%3E) [NC,OR]
# Block any script trying to set a PHP GLOBALS variable via URL.
RewriteCond %{QUERY_STRING} GLOBALS(=|\[|\%[0-9A-Z]{0,2}) [OR]
# Block any script trying to modify a _REQUEST variable via URL.
RewriteCond %{QUERY_STRING} _REQUEST(=|\[|\%[0-9A-Z]{0,2})
# Return 403 Forbidden header and show the content of the root home page
RewriteRule .* index.php [F]
#
## End - Rewrite rules to block out some common exploits.

## Begin - Custom redirects
#
# If you need to redirect some pages, or set a canonical non-www to
# www redirect (or vice versa), place that code here. Ensure those
# redirects use the correct RewriteRule syntax and the [R=301,L] flags.
#
## End - Custom redirects

##
# Uncomment the following line if your webserver's URL
# is not directly related to physical file paths.
# Update Your Joomla! Directory (just / for root).
##

RewriteBase /

## Begin - Joomla! core SEF Section.
#
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
#
# If the requested path and file is not /index.php and the request
# has not already been internally rewritten to the index.php script
RewriteCond %{REQUEST_URI} !^/index\.php
# and the requested path and file doesn't directly match a physical file
RewriteCond %{REQUEST_FILENAME} !-f
# and the requested path and file doesn't directly match a physical folder
RewriteCond %{REQUEST_FILENAME} !-d
# internally rewrite the request to the index.php script
RewriteRule .* index.php [L]
#
## End - Joomla! core SEF Section.