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.
{
    if (!CanGetAddresses(internal)) {
        return false;
    }
    CKeyPool keypool;
    {
        LOCK(cs_KeyStore);
        int64_t nIndex;
        if (!ReserveKeyFromKeyPool(nIndex, keypool, internal) && !m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
            if (m_storage.IsLocked()) return false;
            WalletBatch batch(m_storage.GetDatabase());
            result = GenerateNewKey(batch, internal);
            return true;
        }
        KeepDestination(nIndex, type);
        result = keypool.vchPubKey;
    }
    return true;
}
bool LegacyScriptPubKeyMan::ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool, bool fRequestedInternal)