Endless spinning in 14.0.3

Nextcloud version 14.0.3:
Operating system and version Debian 8:
Apache 2.4.10:
PHP version (eg, 7.0.32):

After upgrading to 14.0.3 the UI is not working anymore, i.e. we get an endless spinner and the content of the folders is not loaded. We observed this behaviour in almost every major browser (Google Chrome, Firefox and Safari) in Linux, MacOS and Windows. We managed to load the content of the folders only via the Edge browser in Windows 10, but the rest is not loading in any operation system.

We did flush the caches on every browser and reloaded the pages, logged out, logged in again, but the issue persists. We never had problems like this.

The native OS clients are not affected by this issue, and sync is working as expected. So, we guess it’s a UI problem.

Steps to replicate it:

  1. Have a running version of 13.0.6.1
  2. Ensure that the UI is working as expected.
  3. Upgrade to 14.0.3 via the stable update channel (we used and have been using the web updater since the 9.x versions with no problems)
  4. Ensure that the UI is working as expected after the upgrade to 14.0.3.

The output of config.php file:

<?php
$CONFIG = array (
  'instanceid' => '[obfuscated]',
  'passwordsalt' => '[obfuscated]',
  'secret' => '[obfuscated]',
  'trusted_domains' => 
  array (
    0 => '[obfuscated].invalid.tld',
  ),
  'datadirectory' => '/[obfuscated]/path/to/data',
  'overwrite.cli.url' => 'https://somedomain.invalid.tld',
  'dbtype' => 'mysql',
  'version' => '14.0.3.0',
  'dbname' => '[obfuscated]',
  'dbhost' => 'localhost',
  'dbtableprefix' => 'oc_',
  'dbuser' => '[obfuscated]',
  'dbpassword' => '[obfuscated]',
  'logtimezone' => 'UTC',
  'installed' => true,
  'updater.release.channel' => 'stable',
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
);

The output of Nextcloud Admin > Logging and Apache are available if you need them.