zabbix_agentd didn't handle server requests correctly while multiple DNS records are used.

It does mean that:

• we've set the DNS record with multiple As (zabbix-servers.company.tld A 1.2.3.4, 1.2.3.5)
• we've set the reverse DNS records for both of this IP addresses to same domain (1.2.3.4 PTR zabbix-servers.company.tld; 1.2.3.5 PTR zabbix-servers.company.tld)
• we've set the zabbix_agentd Server option to this hostname (zabbix-servers.company.tld)

As result, zabbix_agentd refuse several servers requests (approximately 50%, I suppose that low-level getaddr round-robin is used).