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.
{
    assert(!m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS));
    assert(!m_storage.IsWalletFlagSet(WALLET_FLAG_BLANK_WALLET));
    AssertLockHeld(cs_KeyStore);
    bool fCompressed = m_storage.CanSupportFeature(FEATURE_COMPRPUBKEY); 
    CKey secret;
    
    int64_t nCreationTime = GetTime();
    CKeyMetadata metadata(nCreationTime);
    
    if (IsHDEnabled()) {
        DeriveNewChildKey(batch, metadata, secret, (m_storage.CanSupportFeature(FEATURE_HD_SPLIT) ? internal : false));
    } else {
        secret.MakeNewKey(fCompressed);
    }
    
    if (fCompressed) {
        m_storage.SetMinVersion(FEATURE_COMPRPUBKEY);
    }
    CPubKey pubkey = secret.GetPubKey();
    assert(secret.VerifyPubKey(pubkey));
    mapKeyMetadata[pubkey.GetID()] = metadata;
    UpdateTimeFirstKey(nCreationTime);
    if (!AddKeyPubKeyWithDB(batch, secret, pubkey)) {
        throw std::runtime_error(std::string(__func__) + ": AddKey failed");
    }
    return pubkey;
}
const uint32_t BIP32_HARDENED_KEY_LIMIT = 0x80000000;
void LegacyScriptPubKeyMan::DeriveNewChildKey(WalletBatch &batch, CKeyMetadata& metadata, CKey& secret, bool internal)