Cannot understand why APF Firewall blocks a certain IP address
 

I am running APF 9.6. There is an IP address I cannot ping if APF is enabled. But it's OK if I stop APF. The IP is not listed in /etc/apf/deny_hosts.rules. It doesn't help if I add the IP to allow_hosts either. I have also tried disabling realtime lookups: USE_DS="0" USE_DROP="0"