Mediawiki LDAPGroups causing errors

I have some trouble setting up LDAPGroups on Mediawiki LTS 1.35.8. Since the discussion site to this extension seems quite inactive, I want to try my luck here.

I've set up LDAPProvider successfully without any problems. But once I activate LDAPGroups it gives me the error

Original exception: [85942cc925c78b2bb06ab606] /index.php/Hauptseite MediaWiki\Extension\LDAPProvider\LDAPNoDomainConfigException from line 60 of /var/www/mediawiki/extensions/LDAPProvider/src/DomainConfigFactory.php: No configuration available for domain 'domain'!

Now I can replace "LDAP" in the ldapprovider.json with the domain, that's also actually in the table mediawikildap_domains, but that only changes the error to

[a3278aaca2ec924fb8299178] /index.php/Hauptseite TypeError from line 47 of /var/www/mediawiki/includes/config/HashConfig.php: Argument 1 passed to HashConfig::__construct() must be of the type array, null given, called in /var/www/mediawiki/extensions/LDAPProvider/src/DomainConfigFactory.php on line 74

Backtrace:

#0 /var/www/mediawiki/extensions/LDAPProvider/src/DomainConfigFactory.php(74): HashConfig->__construct() #1 /var/www/mediawiki/extensions/LDAPProvider/src/Hook/UserLoadAfterLoadFromSession.php(154): MediaWiki\Extension\LDAPProvider\DomainConfigFactory->factory() #2 /var/www/mediawiki/extensions/LDAPProvider/src/Hook/UserLoadAfterLoadFromSession.php(102): MediaWiki\Extension\LDAPProvider\Hook\UserLoadAfterLoadFromSession->setSuitableDomainConfig() #3 /var/www/mediawiki/extensions/LDAPProvider/src/Hook/UserLoadAfterLoadFromSession.php(90): MediaWiki\Extension\LDAPProvider\Hook\UserLoadAfterLoadFromSession->process() #4 /var/www/mediawiki/includes/HookContainer/HookContainer.php(329): MediaWiki\Extension\LDAPProvider\Hook\UserLoadAfterLoadFromSession::callback() #5 /var/www/mediawiki/includes/HookContainer/HookContainer.php(132): MediaWiki\HookContainer\HookContainer->callLegacyHook() #6 /var/www/mediawiki/includes/HookContainer/HookRunner.php(4348): MediaWiki\HookContainer\HookContainer->run() #7 /var/www/mediawiki/includes/user/User.php(393): MediaWiki\HookContainer\HookRunner->onUserLoadAfterLoadFromSession() #8 /var/www/mediawiki/includes/user/User.php(2156): User->load() #9 /var/www/mediawiki/includes/MediaWiki.php(594): User->getName() #10 /var/www/mediawiki/includes/MediaWiki.php(545): MediaWiki->setDBProfilingAgent() #11 /var/www/mediawiki/index.php(53): MediaWiki->run() #12 /var/www/mediawiki/index.php(46): wfIndexMain() #13 {main}

I already tested if the config added to ldapprovider.json makes any trouble, but everything loads fine as long as LDAPGroups is disabled. Now what am I doing wrong?

Excerpt from LocalSettings.php:

# LDAP-Authentifizierung
wfLoadExtension( 'LDAPProvider' );
$LDAPProviderDomainConfigs = "/var/www/mediawiki/ldapprovider.json";
wfLoadExtension( 'PluggableAuth' );
$wgPluggableAuth_EnableLocalLogin = false;
$wgPluggableAuth_ButtonLabel = "Anmelden";
wfLoadExtension( 'LDAPAuthentication2' );
$LDAPAuthentication2UsernameNormalizer = 'strtolower';
wfLoadExtension( 'LDAPGroups' );

Excerpt from the ldapprovider.json where I added the config

"groupsync": {
"mechanism": "mappedgroups",
"mapping": {
"sysop": "cn=sudoers,ou=groups,dc=domain,dc=de"
}
}

Our setup: