The login failure daemon can crash if you are monitoring a lot of domains in Plesk and are reaching the open file limit for your server. To raise the limit:
Edit the login failure daemon systemd service:
systemctl edit lfd.service
Add the following to the override.conf file:
[Service]
LimitNOFILE=65536
Reload systemd:
systemctl daemon-reload
Restart the LFD service:
systemctl restart lfd.service