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.
public:
    unsigned int nKeys{0};
    unsigned int nCKeys{0};
    unsigned int nWatchKeys{0};
    unsigned int nKeyMeta{0};
    unsigned int m_unknown_records{0};
    bool fIsEncrypted{false};
    bool fAnyUnordered{false};
    std::vector<uint256> vWalletUpgrade;
    std::map<OutputType, uint256> m_active_external_spks;
    std::map<OutputType, uint256> m_active_internal_spks;
    std::map<uint256, DescriptorCache> m_descriptor_caches;
    std::map<std::pair<uint256, CKeyID>, CKey> m_descriptor_keys;
    std::map<std::pair<uint256, CKeyID>, std::pair<CPubKey, std::vector<unsigned char>>> m_descriptor_crypt_keys;
    CWalletScanState() {