When running walletpassphrase on a large wallet.dat (ie about 300,000 segwit P2SH addresses) the command sometimes takes a very long time, and if command is run multiple times at once (while running slow) it causes bitcoin core to freeze (stops syncing and requires kill -9 to stop/restart)

During the locked up walletpassphrase commands being run the following messages start to appear in the debug.log:

`018-01-24 01:01:04 socket sending timeout: 1201s`

Note that this problem is intermittent, so sometimes the command runs instantly, other times it takes a few minutes, and other times it completely freezes the node.
CDataStream ssValue(SER_DISK, CLIENT_VERSION);
            int ret = m_batch.ReadAtCursor(pcursor, ssKey, ssValue);
            if (ret == DB_NOTFOUND)
                break;
            else if (ret != 0)
            {
                LogPrintf("Error reading next record from wallet database\n");
                return DBErrors::CORRUPT;
            }
            std::string strType;
            ssKey >> strType;
            if (strType == DBKeys::TX) {
                uint256 hash;
                ssKey >> hash;
                vTxHash.push_back(hash);
                vWtx.emplace_back(nullptr , nullptr );
                ssValue >> vWtx.back();
            }
        }
        pcursor->close();
    }
    catch (const boost::thread_interrupted&) {
        throw;
    }
    catch (...) {
        result = DBErrors::CORRUPT;
    }
    return result;
}
DBErrors WalletBatch::ZapSelectTx(std::vector<uint256>& vTxHashIn, std::vector<uint256>& vTxHashOut)