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.
{
    LOCK(cs_KeyStore);
    WatchKeyMap::const_iterator it = mapWatchKeys.find(address);
    if (it != mapWatchKeys.end()) {
        pubkey_out = it->second;
        return true;
    }
    return false;
}
bool LegacyScriptPubKeyMan::GetPubKey(const CKeyID &address, CPubKey& vchPubKeyOut) const
{
    LOCK(cs_KeyStore);
    if (!m_storage.HasEncryptionKeys()) {
        if (!FillableSigningProvider::GetPubKey(address, vchPubKeyOut)) {
            return GetWatchPubKey(address, vchPubKeyOut);
        }
        return true;
    }
    CryptedKeyMap::const_iterator mi = mapCryptedKeys.find(address);
    if (mi != mapCryptedKeys.end())
    {
        vchPubKeyOut = (*mi).second.first;
        return true;
    }
    
    return GetWatchPubKey(address, vchPubKeyOut);
}
CPubKey LegacyScriptPubKeyMan::GenerateNewKey(WalletBatch &batch, bool internal)