diff --git a/weed/topology/topology.go b/weed/topology/topology.go
index b99bbd816..ddba44d2d 100644
--- a/weed/topology/topology.go
+++ b/weed/topology/topology.go
@@ -586,6 +586,19 @@ func (t *Topology) SyncDataNodeRegistration(volumes []*master_pb.VolumeInformati
 		}
 		diskType := types.ToDiskType(v.DiskType)
 		vl := t.GetVolumeLayout(v.Collection, v.ReplicaPlacement, v.Ttl, diskType)
+		// Self-heal: a volume reported by the data node but missing from the
+		// lookup index is re-registered. This repairs the split left by a
+		// disconnect/reconnect race, where UnRegisterDataNode dropped the volume
+		// from vid2location but the reconnecting full heartbeat skipped it
+		// (still in the disk map, so UpdateVolumes did not report it as new).
+		// Without this, the volume stays visible in volume.list/admin UI yet
+		// LookupVolume returns "volume id not found".
+		if !vl.HasDataNode(v.Id, dn) {
+			// vl is already resolved above; call it directly instead of
+			// RegisterVolumeLayout, which would repeat the GetVolumeLayout lookup.
+			vl.RegisterVolume(&v, dn)
+			vl.EnsureCorrectWritables(&v)
+		}
 		if vl.UpdateVolumeSize(v.Id, v.Size, v.CompactRevision) {
 			vl.AdjustActiveVolumeCountAfterRecovery(v.Id)
 		}
diff --git a/weed/topology/topology_test.go b/weed/topology/topology_test.go
index 415a7198d..99124a600 100644
--- a/weed/topology/topology_test.go
+++ b/weed/topology/topology_test.go
@@ -573,3 +573,56 @@ func TestLookupDataNodeByAddress(t *testing.T) {
 		t.Fatalf("address must be unregistered after UnRegisterDataNode, got %v", got)
 	}
 }
+
+// TestSyncDataNodeRegistrationReRegistersMissingVolume reproduces the divergence
+// where a volume present on a data node (shown by volume.list / admin UI) is
+// missing from the lookup index, which surfaces as "volume id not found" on
+// LookupVolume. SetVolumeUnavailable (used by
+// UnRegisterDataNode on a disconnect) drops the volume from the index, and the
+// reconnecting full heartbeat used to skip it because it was no longer "new" to
+// the disk map. The full heartbeat now self-heals.
+func TestSyncDataNodeRegistrationReRegistersMissingVolume(t *testing.T) {
+	topo := NewTopology("weedfs", sequence.NewMemorySequencer(), 32*1024, 5, false)
+
+	dc := topo.GetOrCreateDataCenter("dc1")
+	rack := dc.GetOrCreateRack("rack1")
+	dn := rack.GetOrCreateDataNode("127.0.0.1", 34534, 0, "127.0.0.1", "", map[string]uint32{"": 25})
+
+	vid := needle.VolumeId(18994)
+	volumeMessage := &master_pb.VolumeInformationMessage{
+		Id:               uint32(vid),
+		Size:             100,
+		Collection:       "drr",
+		ReplicaPlacement: uint32(0),
+		Version:          uint32(needle.GetCurrentVersion()),
+		Ttl:              0,
+	}
+
+	// Initial full heartbeat registers the volume in the lookup index.
+	topo.SyncDataNodeRegistration([]*master_pb.VolumeInformationMessage{volumeMessage}, dn)
+	if got := topo.Lookup("", vid); len(got) != 1 {
+		t.Fatalf("after registration: lookup %d got %v, want 1 location", vid, got)
+	}
+
+	// Drop the volume from the index the way UnRegisterDataNode does, but leave
+	// it in the data node's disk map (the reconnecting heartbeat did not report
+	// it as new).
+	rp, _ := super_block.NewReplicaPlacementFromString("000")
+	vl := topo.GetVolumeLayout("drr", rp, needle.EMPTY_TTL, types.HardDriveType)
+	vl.SetVolumeUnavailable(dn, vid)
+
+	// The empty entry must be removed, otherwise Lookup returns a non-nil empty
+	// list that still reads as "not found".
+	if got := topo.Lookup("", vid); got != nil {
+		t.Fatalf("after SetVolumeUnavailable: expected lookup miss, got %v", got)
+	}
+	if _, err := dn.GetVolumesById(vid); err != nil {
+		t.Fatalf("volume %d should still be in the data node disk map: %v", vid, err)
+	}
+
+	// The next full heartbeat re-registers the volume even though it is not new.
+	topo.SyncDataNodeRegistration([]*master_pb.VolumeInformationMessage{volumeMessage}, dn)
+	if got := topo.Lookup("", vid); len(got) != 1 {
+		t.Fatalf("after self-heal: lookup %d got %v, want 1 location", vid, got)
+	}
+}
diff --git a/weed/topology/volume_layout.go b/weed/topology/volume_layout.go
index b25097e71..2beedd82e 100644
--- a/weed/topology/volume_layout.go
+++ b/weed/topology/volume_layout.go
@@ -502,6 +502,25 @@ func (vl *VolumeLayout) Lookup(vid needle.VolumeId) []*DataNode {
 	return nil
 }
 
+// HasDataNode reports whether the layout already lists dn as a location for vid.
+// Used to detect a volume that is present on a data node but missing from the
+// lookup index, so it can be re-registered.
+func (vl *VolumeLayout) HasDataNode(vid needle.VolumeId, dn *DataNode) bool {
+	vl.accessLock.RLock()
+	defer vl.accessLock.RUnlock()
+
+	location, ok := vl.vid2location[vid]
+	if !ok {
+		return false
+	}
+	for _, n := range location.list {
+		if n.Ip == dn.Ip && n.Port == dn.Port {
+			return true
+		}
+	}
+	return false
+}
+
 func (vl *VolumeLayout) ListVolumeServers() (nodes []*DataNode) {
 	vl.accessLock.RLock()
 	defer vl.accessLock.RUnlock()
@@ -750,10 +769,21 @@ func (vl *VolumeLayout) SetVolumeUnavailable(dn *DataNode, vid needle.VolumeId)
 		if location.Remove(dn) {
 			vl.readonlyVolumes.Remove(vid, dn)
 			vl.oversizedVolumes.Remove(vid, dn)
+			wasWritable := false
 			if location.Length() < vl.rp.GetCopyCount() {
 				glog.V(0).Infoln("Volume", vid, "has", location.Length(), "replica, less than required", vl.rp.GetCopyCount())
-				return vl.removeFromWritable(vid)
+				wasWritable = vl.removeFromWritable(vid)
 			}
+			if location.Length() == 0 {
+				// Drop the now-empty entry. Otherwise Lookup returns a non-nil
+				// empty location list, which surfaces as "volume id not found"
+				// even though the volume still appears in volume.list/admin UI.
+				// Mirrors UnRegisterVolume.
+				delete(vl.vid2location, vid)
+				delete(vl.sizeTracking, vid)
+				vl.removeFromCrowded(vid)
+			}
+			return wasWritable
 		}
 	}
 	return false