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Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
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
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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): 17.0.3
Operating system and version (eg, Ubuntu 17.04): Ubuntu 18.04.4 LTS
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.29
PHP version (eg, 7.1): 7.2.24
The issue you are facing:
I can’t update my apps using neither occ app:update all nor using the Apps menu. occ app:update all it shows nothing and the Apps menu would only show ‘Your Apps’, ‘Active Apps’, ‘Disable Apps’ and ‘App bandies’ nothing else. I got the notification to update a few of my apps but if I click on them from the notification bell, it goes to Apps menu loads for a few seconds and stays in that empty page.
Is this the first time you’ve seen this error? (Y/N): Y
The output of your Nextcloud log in Admin > Logging:
{"reqId":"h22rXLagF52X0PAQ8WtP","level":3,"time":"2020-03-02T13:46:29+00:00","remoteAddr":"IP","user":"USER","app":"no app in context","method":"GET","url":"/nextcloud/apps/logreader/poll?lastReqId=jQbMnyqCJYAyy5EWXz1t","message":{"Exception":"InvalidArgumentException","Message":"Notifier Deck (id: deck) is not considered because it is using the old way to register.","Code":0,"Trace":[{"file":"/var/www/nextcloud/apps/deck/lib/AppInfo/Application.php","line":149,"function":"registerNotifier","class":"OC\\Notification\\Manager","type":"->","args":[{"__class__":"Closure"},{"__class__":"Closure"}]},{"file":"/var/www/nextcloud/apps/deck/appinfo/app.php","line":30,"function":"registerNotifications","class":"OCA\\Deck\\AppInfo\\Application","type":"->","args":[]},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":265,"args":["/var/www/nextcloud/apps/deck/appinfo/app.php"],"function":"require_once"},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":155,"function":"requireAppFile","class":"OC_App","type":"::","args":[{"__class__":"OCA\\Deck\\AppInfo\\Application"}]},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":128,"function":"loadApp","class":"OC_App","type":"::","args":["deck"]},{"file":"/var/www/nextcloud/apps/dav/appinfo/app.php","line":30,"function":"loadApps","class":"OC_App","type":"::","args":[["dav"]]},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":265,"args":["/var/www/nextcloud/apps/dav/appinfo/app.php"],"function":"require_once"},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":155,"function":"requireAppFile","class":"OC_App","type":"::","args":["dav"]},{"file":"/var/www/nextcloud/lib/private/legacy/app.php","line":128,"function":"loadApp","class":"OC_App","type":"::","args":["dav"]},{"file":"/var/www/nextcloud/lib/base.php","line":982,"function":"loadApps","class":"OC_App","type":"::","args":[]},{"file":"/var/www/nextcloud/index.php","line":42,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/var/www/nextcloud/lib/private/Notification/Manager.php","Line":86,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.122 Safari/537.36","version":"17.0.3.1","id":"5e5d0e35d0b88"}
The error is InvalidArgumentException","Message":"Notifier Deck (id: deck) is not considered because it is using the old way to register. And this repeats for all the apps.
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => 'oc3waeb11',
'passwordsalt' => '',
'secret' => '',
'trusted_domains' =>
array (
0 => '$DOMAIN',
),
'datadirectory' => '/var/www/nextcloud/data',
'overwrite.cli.url' => 'PROTO://DOMAIN.TLD/nextcloud',
'htaccess.RewriteBase' => '/nextcloud',
'dbtype' => 'pgsql',
'version' => '17.0.3.1',
'dbname' => 'nextcloud',
'dbhost' => 'localhost:5432',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => '$PG_USER',
'dbpassword' => '$PG_PASS',
'installed' => true,
'mail_smtpmode' => 'smtp',
'mail_smtpauthtype' => 'LOGIN',
'theme' => '',
'maintenance' => false,
'mail_smtphost' => 'smtp.gmail.com',
'mail_smtpport' => '465',
'mail_smtpauth' => 1,
'mail_smtpname' => '$SMTP_USER',
'mail_smtppassword' => '$SMTP_PASS',
'mail_smtpsecure' => 'ssl',
'mail_from_address' => '$DOMAIN,
'updater.release.channel' => 'stable',
'loglevel' => 2,
'data-fingerprint' => '72109552534eb13e0b5f2d97',
);
I would be very grateful if anyone can help me solve this. Thanks in advance!