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 ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool);
    CBlockIndex* AddToBlockIndex(const CBlockHeader& block);
    
    CBlockIndex * InsertBlockIndex(const uint256& hash);
    void CheckBlockIndex(const Consensus::Params& consensusParams);
    void InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state);
    CBlockIndex* FindMostWorkChain();
    bool ReceivedBlockTransactions(const CBlock &block, CValidationState& state, CBlockIndex *pindexNew, const CDiskBlockPos& pos, const Consensus::Params& consensusParams);
    bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params);
} g_chainstate;
CCriticalSection cs_main;
BlockMap& mapBlockIndex = g_chainstate.mapBlockIndex;
CChain& chainActive = g_chainstate.chainActive;
CBlockIndex *pindexBestHeader = nullptr;
CWaitableCriticalSection g_best_block_mutex;
CConditionVariable g_best_block_cv;
uint256 g_best_block;
int nScriptCheckThreads = 0;
std::atomic_bool fImporting(false);
std::atomic_bool fReindex(false);
bool fTxIndex = false;
bool fHavePruned = false;
bool fPruneMode = false;
bool fIsBareMultisigStd = DEFAULT_PERMIT_BAREMULTISIG;
bool fRequireStandard = true;
bool fCheckBlockIndex = false;
bool fCheckpointsEnabled = DEFAULT_CHECKPOINTS_ENABLED;
size_t nCoinCacheUsage = 5000 * 300;
uint64_t nPruneTarget = 0;
int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;