Also show policer indicates huge drop;

root> show policer __default_arp_policer__

Policers:

Name                                                                           Bytes             Packets

__default_arp_policer__                                                 34820875040           828756523

root@> show dhcp relay statistics verbose

Packets dropped:

   Total                     232225

   Invalid server address    228461

   Interface not configured  71

   Send error                1

   dhcp-service total        3692

Please apply arp policer per interface and to validate from where it's coming from.

Apply arp policer for all interfaces with family inet, using below procedure:

https://www.juniper.net/documentation/us/en/software/junos/routing-policy/topics/example/example-configuring-arp-policer.html

or

set firewall policer ARP_Policer if-exceeding bandwidth-limit 8k

set firewall policer ARP_Policer if-exceeding burst-size-limit 1500

set firewall policer ARP_Policer then discard

set interfaces aeXX family inet policer arp ARP_Policer