private void reactToTTDReachedEvent(final boolean ttdReached) {
    if (started.get() && ttdReached) {
      LOG.info("Block propagation was running, then ttd reached");
    } else if (!started.get()) {
      start();
    }
  }
Try to request the lowest ancestor for the given pending block or process the descendants if
the ancestor is already in the chain
ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/sync/BlockPropagationManager.java