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.
std::unique_ptr<SigningProvider> GetSolvingProvider(const CScript& script) const override;
    bool CanProvide(const CScript& script, SignatureData& sigdata) override;
    bool SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, std::string>& input_errors) const override;
    SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const override;
    TransactionError FillPSBT(PartiallySignedTransaction& psbt, int sighash_type = 1 , bool sign = true, bool bip32derivs = false) const override;
    uint256 GetID() const override;
    void SetType(OutputType type, bool internal) override;
    
    std::map<CKeyID, CKeyMetadata> mapKeyMetadata GUARDED_BY(cs_KeyStore);
    
    std::map<CScriptID, CKeyMetadata> m_script_metadata GUARDED_BY(cs_KeyStore);
    
    bool AddKeyPubKey(const CKey& key, const CPubKey &pubkey) override;
    
    bool LoadKey(const CKey& key, const CPubKey &pubkey);
    
    bool AddCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret);
    
    bool LoadCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret);
    void UpdateTimeFirstKey(int64_t nCreateTime) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    
    bool LoadCScript(const CScript& redeemScript);
    
    void LoadKeyMetadata(const CKeyID& keyID, const CKeyMetadata &metadata);
    void LoadScriptMetadata(const CScriptID& script_id, const CKeyMetadata &metadata);
    
    CPubKey GenerateNewKey(WalletBatch& batch, bool internal = false) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    
    void SetHDChain(const CHDChain& chain, bool memonly);
    const CHDChain& GetHDChain() const { return hdChain; }