diff --git a/hscontrol/mapper/batcher.go b/hscontrol/mapper/batcher.go
index 6fbefdbe..ce569732 100644
--- a/hscontrol/mapper/batcher.go
+++ b/hscontrol/mapper/batcher.go
@@ -178,10 +178,20 @@ func handleNodeChange(nc nodeConnection, mapper *mapper, r change.Change) error
 	// Send the map response
 	err = nc.send(data)
 	if err != nil {
+		// If the node has no active connections, the data was not
+		// delivered. Do not update lastSentPeers — recording phantom
+		// peer state would corrupt future computePeerDiff calculations,
+		// causing the node to miss peer additions or removals after
+		// reconnection.
+		if errors.Is(err, errNoActiveConnections) {
+			return nil
+		}
+
 		return fmt.Errorf("sending map response to node %d: %w", nodeID, err)
 	}
 
-	// Update peer tracking after successful send
+	// Update peer tracking only after confirmed delivery to at
+	// least one active connection.
 	nc.updateSentPeers(data)
 
 	return nil
diff --git a/hscontrol/mapper/batcher_unit_test.go b/hscontrol/mapper/batcher_unit_test.go
index 54172522..bef897fe 100644
--- a/hscontrol/mapper/batcher_unit_test.go
+++ b/hscontrol/mapper/batcher_unit_test.go
@@ -339,8 +339,9 @@ func TestMultiChannelSend_ZeroConnections(t *testing.T) {
 
 	err := mc.send(testMapResponse())
 
-	require.NoError(t, err,
-		"sending to node with 0 connections should succeed silently (rapid reconnection scenario)")
+	require.ErrorIs(t, err, errNoActiveConnections,
+		"sending to node with 0 connections should return errNoActiveConnections "+
+			"so callers skip updateSentPeers (prevents phantom peer state)")
 }
 
 func TestMultiChannelSend_NilData(t *testing.T) {
diff --git a/hscontrol/mapper/node_conn.go b/hscontrol/mapper/node_conn.go
index 87d61544..faa893fa 100644
--- a/hscontrol/mapper/node_conn.go
+++ b/hscontrol/mapper/node_conn.go
@@ -1,6 +1,7 @@
 package mapper
 
 import (
+	"errors"
 	"fmt"
 	"strconv"
 	"sync"
@@ -16,6 +17,12 @@ import (
 	"tailscale.com/tailcfg"
 )
 
+// errNoActiveConnections is returned by send when a node has no active
+// connections (disconnected but kept in the batcher for rapid reconnection).
+// Callers must not update peer tracking state (lastSentPeers) after this
+// error because the data was never delivered to any client.
+var errNoActiveConnections = errors.New("no active connections")
+
 // connectionEntry represents a single connection to a node.
 type connectionEntry struct {
 	id       string // unique connection ID
@@ -243,7 +250,7 @@ func (mc *multiChannelNodeConn) send(data *tailcfg.MapResponse) error {
 		mc.log.Trace().
 			Msg("send: no active connections, skipping")
 
-		return nil
+		return errNoActiveConnections
 	}
 
 	// Copy the slice so we can release the read lock before sending.