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.
bool LoadWatchOnly(const CScript &dest);
    
    bool HaveWatchOnly(const CScript &dest) const;
    
    bool HaveWatchOnly() const;
    
    bool RemoveWatchOnly(const CScript &dest);
    bool AddWatchOnly(const CScript& dest, int64_t nCreateTime) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    
    bool GetWatchPubKey(const CKeyID &address, CPubKey &pubkey_out) const;
    
    bool HaveKey(const CKeyID &address) const override;
    bool GetKey(const CKeyID &address, CKey& keyOut) const override;
    bool GetPubKey(const CKeyID &address, CPubKey& vchPubKeyOut) const override;
    bool AddCScript(const CScript& redeemScript) override;
    bool GetKeyOrigin(const CKeyID& keyid, KeyOriginInfo& info) const override;
    
    void LoadKeyPool(int64_t nIndex, const CKeyPool &keypool);
    bool NewKeyPool();
    void MarkPreSplitKeys() EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    bool ImportScripts(const std::set<CScript> scripts, int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    bool ImportPrivKeys(const std::map<CKeyID, CKey>& privkey_map, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    bool ImportPubKeys(const std::vector<CKeyID>& ordered_pubkeys, const std::map<CKeyID, CPubKey>& pubkey_map, const std::map<CKeyID, std::pair<CPubKey, KeyOriginInfo>>& key_origins, const bool add_keypool, const bool internal, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);
    bool ImportScriptPubKeys(const std::set<CScript>& script_pub_keys, const bool have_solving_data, const int64_t timestamp) EXCLUSIVE_LOCKS_REQUIRED(cs_KeyStore);