Upgrade 21.0.1 > 21.0.2: json issue

Support intro

Nextcloud version (eg, 20.0.5): 21.0.2
Operating system and version (eg, Ubuntu 20.04): 20.04
Apache or nginx version (eg, Apache 2.4.25): 2.4.29
PHP version (eg, 7.4): 7.4

The output of your Nextcloud log in Admin > Logging:

{"reqId":"EV5fmbCocRDZx5QfP1ER","level":2,"time":"2021-05-21T20:14:45+00:00","remoteAddr":"","user":"herve","app":"lib","method":"GET","url":"/index.php","message":"AppManger::checkAppForUser - can't decode group IDs: NULL - json error code: 4","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36","version":""}

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

array (
    0 => '',
    1 => 'xxxxxxxx.fr',
    2 => 'xxxxxxxxxxx.fr',
    3 => 'localhost',
  'datadirectory' => '/var/www/html/nextcloud/data',
  'dbtype' => 'mysql',
  'version' => '',
  'overwrite.cli.url' => 'http://localhost/nextcloud',
  'dbname' => 'nextcloud',
  'dbhost' => 'xxxxxxxxxxxxxxxx',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'oc_herve',
  'dbpassword' => 'xxxxxxxxxxxxxxxxx',
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'installed' => true,
  'auth.bruteforce.protection.enabled' => false,
  'integrity.check.disabled' => true,
  'default_phone_region' => 'FR',
  'app_install_overwrite' => 
  array (
    0 => 'occweb',
    1 => 'breezedark',
    2 => 'documentserver_community',
    3 => 'ocdownloader',
    4 => 'files_trackdownloads',
    5 => 'cookbook',
    6 => 'onlyoffice',
    7 => 'files_opds',
  'mail_smtpmode' => 'smtp',
  'mail_smtpsecure' => 'tls',
  'mail_sendmailmode' => 'smtp',
  'mail_from_address' => 'cloud',
  'mail_domain' => 'xxxxxxxxxxxxxxxx',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtphost' => 'xxxxxxxxxxxxxxt',
  'mail_smtpport' => '587',
  'mail_smtpauth' => 1,
  'mail_smtpname' => 'xxxxxxxxxxxxxxxx',
  'mail_smtppassword' => 'xxxxxxxxxxxxxx',
  'theme' => '',
  'loglevel' => 2,
  'updater.release.channel' => 'stable',
  'maintenance' => false,
  'updater.secret' => xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',

After proceeding upgrade to 21.0.2, I face to an internal error issue (in french: Le serveur est incapable d'exécuter votre requête.

Si cela se reproduit, veuillez envoyer les détails techniques ci-dessous à l'administrateur du serveur.)

After a simple log research, I found a JSON error: message":"AppManger::checkAppForUser - can't decode group IDs: NULL - json error code: 4"

Is there any way to solve it? Thanks!

Small addon: the way to access to my data is https://mywebsite.fr/index.php/apps/dashboard/ instead of https://mywebsite.fr

Oups the contingency procedure to access data is limited. If y click on parameters, I face to the same issue. If there is no solution, I will use the workaround access to save data an rebuild a nextcloud server from scratch.
Except, of course, if somebody on this forum has a genious idea…

It happends also to me, on a nextcloud vm
I’ve disabled all and every app one by one via GUI
and then re-enable one by one always via GUI
every time I’ve re-enabled a app the icon has appear again on the top nextcloud bar
now everything works without errors
that was my error repeated hundreds of times
{“reqId”:“xxxxxxxxxxxxxxxxxxxx”,“level”:2,“time”:“2021-06-15T13:09:07+00:00”,“remoteAddr”:“xxxxxxxx”,“user”:“xxxxxxxx”,“app”:“lib”,“method”:“GET”,“url”:"/apps/files/",“message”:“AppManger::checkAppForUser - can’t decode group IDs: Nextcloud or one of the apps require upgrade - only a limited number of commands are available\nYou may use your browser or the occ upgrade command to do the upgrade\nyes - json error code: 4”,“userAgent”:“Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36”,“version”:“”}