Subscribed calendar, no events displayed

Hello !
I added a new subscibed calendar few days ago, but I didn’t see any event of this calendar. I tried with other calendars, and it works. But not for a specific one and I don’t understand why. I tried on a random site to preview my ical link, and it works (http://www.instantcal.com/) but not on NextCloud. Cron TASK are working too.
image

Nextcloud version (eg, 18.0.2): lastest at the date of creation of this post
Operating system and version (eg, Ubuntu 20.04): lastest at the date of creation of this post
Apache or nginx version (eg, Apache 2.4.25): lastest at the date of creation of this post
PHP version (eg, 7.1): lastest at the date of creation of this post

The output of your Nextcloud log in Admin > Logging:
0 errors/warning in logs since 15 days. I added the calendar after that, so there is nothing here.

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

<?php
$CONFIG = array (
  'instanceid' => 'xxxxxxxxxxxxxxxxxxxxx',
  'passwordsalt' => 'xxxxxxxxxxxxxxxxxxxxx',
  'secret' => 'xxxxxxxxxxxxxxxxxxxxx',
  'trusted_domains' => 
  array (
    0 => 'xxxxxxxxxxxxxxxxxxxxx',
  ),
  'datadirectory' => '/var/www/data',
  'dbtype' => 'mysql',
  'version' => '20.0.4.0',
  'overwrite.cli.url' => 'xxxxxxxxxxxxxxxxxxxxx',
  'dbname' => 'xxxxxxxxxxxxxxxxxxxxx',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mysql.utf8mb4' => true,
  'dbuser' => 'xxxxxxxxxxxxxxxxxxxxx',
  'dbpassword' => 'xxxxxxxxxxxxxxxxxxxxx',
  'installed' => true,
  'maintenance' => false,
  'app_install_overwrite' => 
  array (
    0 => 'twofactor_rcdevsopenotp',
    1 => 'files_trackdownloads',
  ),
  'mail_from_address' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtpmode' => 'smtp',
  'mail_sendmailmode' => 'smtp',
  'mail_domain' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtpauthtype' => 'LOGIN',
  'mail_smtpauth' => 1,
  'mail_smtphost' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtpport' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtpname' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtppassword' => 'xxxxxxxxxxxxxxxxxxxxx',
  'mail_smtpsecure' => 'ssl',
  'theme' => '',
  'loglevel' => 2,
  'updater.release.channel' => 'stable',
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'memcache.distributed' => '\\OC\\Memcache\\Redis',
  'redis' => 
  array (
    'host' => 'localhost',
    'port' => 6379,
    'timeout' => 1.5,
  ),
  'appstore.experimental.enabled' => true,
);

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

[Thu Dec 31 00:00:12.507267 2020] [mpm_prefork:notice] [pid 767] AH00163: Apache/2.4.38 (Debian) OpenSSL/1.1.1i configured -- resuming normal operations
[Thu Dec 31 00:00:12.512624 2020] [core:notice] [pid 767] AH00094: Command line: '/usr/sbin/apache2'
[Thu Dec 31 01:45:26.044509 2020] [php7:error] [pid 3697] [client 45.155.205.108:44406] script '/var/www/html/index.php' not found or unable to stat
[Thu Dec 31 19:19:55.176034 2020] [php7:error] [pid 25058] [client 13.66.215.179:61356] script '/var/www/html/xmlrpc.php' not found or unable to stat

is there any setup-message left unsolved under admin-setup-overview?