This Counter64 totals the authentication failures across all current and previous Phase-1 control tunnels, per its description - each incrementing when a peer's identity or credentials couldn't be verified during Phase-1 negotiation. A sudden spike here across many tunnels at once, rather than isolated to one peer, would suggest a shared secret rotation was botched or a certificate authority issue is affecting multiple peers simultaneously. An admin correlating a spike in this counter with a recent pre-shared-key rollout would immediately suspect the new keys weren't correctly applied on both ends.