Unable to install Wordpress in Plesk: move_to_cgroup(): pam_open_session() failed 6: Permission denied

The following error can be found in the /var/log/plesk/panel.log:

CONFIG_TEXT: ERR [extension/wp-toolkit] #0 /opt/psa/admin/plib/modules/wp-toolkit/library/Helper/Util.php(199): Zend_Json::decode('move_to_cgroup(...')
#1 /opt/psa/admin/plib/modules/wp-toolkit/library/Capability/Command/Config.php(119): PleskExt\WpToolkit\Helper\Util::decode('move_to_cgroup(...')
#2 /opt/psa/admin/plib/modules/wp-toolkit/library/Capability/Command/Config.php(55): PleskExt\WpToolkit\Capability\Command\Config->reset()
...
#17 /opt/psa/admin/plib/api-cli/CliUtilityRunner.php(35): CliUtilityRunner->run()
#18 /opt/psa/admin/plib/api-cli/extension.php(4): require_once('/opt/psa/admin/...')
#19 {main}

The following errors can be found in the /var/log/syslog:

CONFIG_TEXT: sshd[13985]: input_userauth_request: invalid user osmc [preauth]
sshd[13985]: pam_unix(sshd:auth): check pass; user unknown
sshd[13985]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=5.188.10.179
suexec[14029]: pam_systemd(plesk_resctrl:session): Failed to create session: Message did not receive a reply (timeout by message bus)
systemd[1]: Starting Session c223 of user jdoe.
systemd[1]: Started Session c223 of user cschlender.
systemd[1]: systemd-logind.service has no holdoff time, scheduling restart.
systemd[1]: Stopping Login Service...
systemd[1]: Starting Login Service...