"no backend has been configured" after creating a new user?

I set up icinga2 last week (without Director) and added passive checks for a number of hosts, and everything was working beautifully. Then I added a new user with limited access - when I logged in with this user, I saw messages everywhere like:

No backend has been configured

#0 /usr/share/icingaweb2/modules/monitoring/library/Monitoring/Backend/MonitoringBackend.php(76): Icinga\Module\Monitoring\Backend\MonitoringBackend::loadConfig()
#1 /usr/share/icingaweb2/modules/monitoring/library/Monitoring/Controller.php(32): Icinga\Module\Monitoring\Backend\MonitoringBackend::instance()
#2 /usr/share/php/Icinga/Web/Controller/ModuleActionController.php(28): Icinga\Module\Monitoring\Controller->moduleInit()
#3 /usr/share/php/Icinga/Web/Controller/ActionController.php(169): Icinga\Web\Controller\ModuleActionController->prepareInit()
#4 /usr/share/php/Icinga/Web/Controller/Dispatcher.php(59): Icinga\Web\Controller\ActionController->__construct()
#5 /usr/share/icingaweb2/library/vendor/Zend/Controller/Front.php(937): Icinga\Web\Controller\Dispatcher->dispatch()
#6 /usr/share/php/Icinga/Application/Web.php(290): Zend_Controller_Front->dispatch()
#7 /usr/share/php/Icinga/Application/webrouter.php(105): Icinga\Application\Web->dispatch()
#8 /usr/share/icingaweb2/public/index.php(4): require_once(String)
#9 {main}

After trying to enable modules for this user, I now also have the problem when I log in as the admin user, where there was no problem before.

What did I do wrong? And more importantly, how do I fix it (and get a non-admin user that works)?

This is my configuration:

root@vogon:/etc/icinga2/scripts# icinga2 -V
icinga2 - The Icinga 2 network monitoring daemon (version: r2.13.7-1)

Copyright (c) 2012-2023 Icinga GmbH (https://icinga.com/)
License GPLv2+: GNU GPL version 2 or later <https://gnu.org/licenses/gpl2.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

System information:
  Platform: Debian GNU/Linux
  Platform version: 11 (bullseye)
  Kernel: Linux
  Kernel version: 5.10.0-13-amd64
  Architecture: x86_64

Build information:
  Compiler: GNU 10.2.1
  Build host: runner-hh8q3bz2-project-575-concurrent-0
  OpenSSL version: OpenSSL 1.1.1n  15 Mar 2022

Application information:

General paths:
  Config directory: /etc/icinga2
  Data directory: /var/lib/icinga2
  Log directory: /var/log/icinga2
  Cache directory: /var/cache/icinga2
  Spool directory: /var/spool/icinga2
  Run directory: /run/icinga2

Old paths (deprecated):
  Installation root: /usr
  Sysconf directory: /etc
  Run directory (base): /run
  Local state directory: /var

Internal paths:
  Package data directory: /usr/share/icinga2
  State path: /var/lib/icinga2/icinga2.state
  Modified attributes path: /var/lib/icinga2/modified-attributes.conf
  Objects path: /var/cache/icinga2/icinga2.debug
  Vars path: /var/cache/icinga2/icinga2.vars
  PID path: /run/icinga2/icinga2.pid

root@vogon:/etc/icinga2/scripts# icingacli module list
MODULE         VERSION   STATE     DESCRIPTION
doc            2.11.4    enabled   Documentation module
icingadb       1.0.2     enabled   Icinga DB Web
monitoring     2.11.4    enabled   Icinga monitoring module
setup          2.11.4    enabled   Setup module

root@vogon:/etc/icinga2/scripts# icinga2 feature list
Disabled features: command compatlog debuglog elasticsearch gelf graphite influxdb influxdb2 livestatus opentsdb perfdata statusdata syslog
Enabled features: api checker icingadb mainlog notification

root@vogon:/etc/icinga2/scripts# icinga2 daemon -C
[2023-03-23 10:38:20 +0000] information/cli: Icinga application loader (version: r2.13.7-1)
[2023-03-23 10:38:20 +0000] information/cli: Loading configuration file(s).
[2023-03-23 10:38:20 +0000] information/ConfigItem: Committing config item(s).
[2023-03-23 10:38:20 +0000] information/ApiListener: My API identity: vogon.comind.io
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 IcingaApplication.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 2 HostGroups.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 8 Hosts.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 FileLogger.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 Downtime.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 Comment.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 CheckerComponent.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 14 Notifications.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 IcingaDB.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 3 Zones.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 Endpoint.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 ApiUser.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 ApiListener.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 NotificationComponent.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 246 CheckCommands.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 UserGroup.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 3 ServiceGroups.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 3 TimePeriods.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 User.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 1 ScheduledDowntime.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 88 Services.
[2023-03-23 10:38:20 +0000] information/ConfigItem: Instantiated 2 NotificationCommands.
[2023-03-23 10:38:21 +0000] information/ScriptGlobal: Dumping variables to file '/var/cache/icinga2/icinga2.vars'
[2023-03-23 10:38:22 +0000] information/cli: Finished validating the configuration file(s).

From the web interface:
Icinga Web 2 Version 	2.11.4
Git commit 	11453bfa92a70a44efbf7f966f5e7f27e9300a28
PHP Version 	7.4.33
Git commit date 	2023-01-26

Loaded Libraries
icinga/icinga-php-library 	0.10.1
icinga/icinga-php-thirdparty 	0.11.0

Loaded Modules
doc 		2.11.4 	Configure
icingadb 		1.0.2 	Configure
monitoring 		2.11.4 	Configure
setup 		2.11.4 	Configure
Copyright © 2013-2023 Icinga GmbH

An update - it seems I somehow managed to wipe out the monitoring, doc and setup module, apparently just by trying to enable the module for my new user - this is my /etc/icingaweb2:

root@vogon:/etc/icingaweb2# ll *
-rw-rw---- 1 www-data icingaweb2   54 Mar 17 17:06 authentication.ini
-rw-rw---- 1 www-data icingaweb2  190 Mar 17 17:06 config.ini
-rw-rw---- 1 www-data icingaweb2   54 Mar 17 17:06 groups.ini
-rw-rw---- 1 www-data icingaweb2  318 Mar 17 17:24 resources.ini
-rw-rw---- 1 www-data icingaweb2  521 Mar 23 10:40 roles.ini

enabledModules:
total 0
lrwxrwxrwx 1 www-data icingaweb2 33 Mar 17 17:06 doc -> /usr/share/icingaweb2/modules/doc
lrwxrwxrwx 1 www-data icingaweb2 38 Mar 17 17:06 icingadb -> /usr/share/icingaweb2/modules/icingadb
lrwxrwxrwx 1 www-data icingaweb2 40 Mar 23 10:20 monitoring -> /usr/share/icingaweb2/modules/monitoring
lrwxrwxrwx 1 www-data icingaweb2 35 Mar 23 10:23 setup -> /usr/share/icingaweb2/modules/setup

modules:
total 4
drwxrws--- 2 www-data icingaweb2 4096 Mar 17 17:06 icingadb/

I don’t know if they were there from the beginning.