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.
return true;
}
bool LegacyScriptPubKeyMan::HavePrivateKeys() const
{
    LOCK(cs_KeyStore);
    return !mapKeys.empty() || !mapCryptedKeys.empty();
}
void LegacyScriptPubKeyMan::RewriteDB()
{
    LOCK(cs_KeyStore);
    setInternalKeyPool.clear();
    setExternalKeyPool.clear();
    m_pool_key_to_index.clear();
    
    
    
}
static int64_t GetOldestKeyTimeInPool(const std::set<int64_t>& setKeyPool, WalletBatch& batch) {
    if (setKeyPool.empty()) {
        return GetTime();
    }
    CKeyPool keypool;
    int64_t nIndex = *(setKeyPool.begin());
    if (!batch.ReadPool(nIndex, keypool)) {
        throw std::runtime_error(std::string(__func__) + ": read oldest key in keypool failed");
    }
    assert(keypool.vchPubKey.IsValid());
    return keypool.nTime;
}
int64_t LegacyScriptPubKeyMan::GetOldestKeyPoolTime() const