Reported here https://github.com/bitcoin/bitcoin/pull/12629#issuecomment-381095603 by @Empact.  I've seen it now in a few different travis jobs, including:

https://travis-ci.org/bitcoin/bitcoin/jobs/366157920
https://travis-ci.org/bitcoin/bitcoin/jobs/366139851

From my initial investigation it seems like there may be an actual bug in block announcement, so I'm  opening this issue to track.
{
    AssertLockHeld(cs_main);
    if (chainActive.Tip() && chainActive.Tip()->GetBlockHash() == pcoinsTip->GetBestBlock()) return true;
    if (pcoinsTip->GetBestBlock().IsNull() && mapBlockIndex.size() == 1) {
        
        
        LogPrintf("%s: Connecting genesis block...\n", __func__);
        CValidationState state;
        if (!ActivateBestChain(state, chainparams)) {
            return false;
        }
    }
    
    CBlockIndex* pindex = LookupBlockIndex(pcoinsTip->GetBestBlock());
    if (!pindex) {
        return false;
    }
    chainActive.SetTip(pindex);
    g_chainstate.PruneBlockIndexCandidates();
    LogPrintf("Loaded best chain: hashBestChain=%s height=%d date=%s progress=%f\n",
        chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(),
        FormatISO8601DateTime(chainActive.Tip()->GetBlockTime()),
        GuessVerificationProgress(chainparams.TxData(), chainActive.Tip()));
    return true;
}
CVerifyDB::CVerifyDB()