message: [sync]error log.
diff: @@ -220,6 +220,7 @@ impl DownloadActor {
  .sync_count
  .with_label_values(&[LABEL_STATE])
  .inc();
  + if !syncing.load(Ordering::Relaxed) {
  syncing.store(true, Ordering::Relaxed);
  match Self::sync_state_and_block_inner(
  self_peer_id.clone(),
  @@ -234,7 +235,7 @@ impl DownloadActor {
  .await
  {
  Err(e) => {
  - debug!("state sync error : {:?}", e);
  + error!("state sync error : {:?}", e);
  syncing.store(false, Ordering::Relaxed);
  Self::sync_state_and_block(
  self_peer_id.clone(),
  @@ -259,6 +260,7 @@ impl DownloadActor {
  }
  }
  }
  + }
  });
  }
  