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.
bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                              bool bypass_limits, const CAmount& nAbsurdFee, std::vector<COutPoint>& coins_to_uncache, bool test_accept)
{
    const CTransaction& tx = *ptx;
    const uint256 hash = tx.GetHash();
    AssertLockHeld(cs_main);
    LOCK(pool.cs); 
    if (pfMissingInputs) {
        *pfMissingInputs = false;
    }
    if (!CheckTransaction(tx, state))
        return false; 
    
    if (tx.IsCoinBase())
        return state.DoS(100, false, REJECT_INVALID, "coinbase");
    
    bool witnessEnabled = IsWitnessEnabled(chainActive.Tip(), chainparams.GetConsensus());
    if (!gArgs.GetBoolArg("-prematurewitness", false) && tx.HasWitness() && !witnessEnabled) {
        return state.DoS(0, false, REJECT_NONSTANDARD, "no-witness-yet", true);
    }
    
    std::string reason;
    if (fRequireStandard && !IsStandardTx(tx, reason, witnessEnabled))
        return state.DoS(0, false, REJECT_NONSTANDARD, reason);