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.
{
    LOCK(cs_main);
    
    
    
    
    if (mapBlockIndex.count(chainparams.GenesisBlock().GetHash()))
        return true;
    try {
        CBlock &block = const_cast<CBlock&>(chainparams.GenesisBlock());
        CDiskBlockPos blockPos = SaveBlockToDisk(block, 0, chainparams, nullptr);
        if (blockPos.IsNull())
            return error("%s: writing genesis block to disk failed", __func__);
        CBlockIndex *pindex = AddToBlockIndex(block);
        CValidationState state;
        if (!ReceivedBlockTransactions(block, state, pindex, blockPos, chainparams.GetConsensus()))
            return error("%s: genesis block not accepted", __func__);
    } catch (const std::runtime_error& e) {
        return error("%s: failed to write genesis block: %s", __func__, e.what());
    }
    return true;
}
bool LoadGenesisBlock(const CChainParams& chainparams)