This Counter64 totals the Phase-2 security association delete requests received across all currently and previously active Phase-1 control tunnels, per its description - each of these represents a peer tearing down one specific IPsec data SA underneath a still-live IKE tunnel. A high rate here across the whole device suggests widespread SA churn, possibly from a network-wide event like a routing change causing many peers to renegotiate their traffic selectors simultaneously. An admin correlating a spike in this global counter with a recent network change would look for what triggered so many peers to delete and presumably re-negotiate their Phase-2 SAs at once.