This is the advice I'm following on that.
AI Overview (Google):
"Yes, you should keep set l3param -implicitACLAllow ENABLED.
"This setting ensures that critical internal system communications (such as high-availability heartbeats, internal cluster synchronization, and control channel commands) bypass your Access Control Lists (ACLs). Setting this parameter to DISABLED risks breaking your High Availability (HA) sync or bricking appliance communications entirely.
"The parameter implicitACLAllow does not allow general public web traffic to bypass your rules. It is specifically designed to safeguard traffic to internal ports (like TCP 3008-3011, UDP 3003, and cluster controls)."