Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            RPCHelpMan{"getbestblockhash",
                "\nReturns the hash of the best (tip) block in the longest blockchain.\n",
                {},
                RPCResult{
            "\"hex\"      (string) the block hash, hex-encoded\n"
                },
                RPCExamples{
                    HelpExampleCli("getbestblockhash", "")
            + HelpExampleRpc("getbestblockhash", "")
                },
            }.ToString());
    LOCK(cs_main);
    return chainActive.Tip()->GetBlockHash().GetHex();
}
void RPCNotifyBlockChange(bool ibd, const CBlockIndex * pindex)