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 (m_storage.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        return false;
    }
    {
        LOCK(cs_KeyStore);
        WalletBatch batch(m_storage.GetDatabase());
        for (const int64_t nIndex : setInternalKeyPool) {
            batch.ErasePool(nIndex);
        }
        setInternalKeyPool.clear();
        for (const int64_t nIndex : setExternalKeyPool) {
            batch.ErasePool(nIndex);
        }
        setExternalKeyPool.clear();
        for (const int64_t nIndex : set_pre_split_keypool) {
            batch.ErasePool(nIndex);
        }
        set_pre_split_keypool.clear();
        m_pool_key_to_index.clear();
        if (!TopUp()) {
            return false;
        }
        WalletLogPrintf("LegacyScriptPubKeyMan::NewKeyPool rewrote keypool\n");
    }
    return true;
}
bool LegacyScriptPubKeyMan::TopUp(unsigned int kpSize)