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);
    bool hd_upgrade = false;
    bool split_upgrade = false;
    if (m_storage.CanSupportFeature(FEATURE_HD) && !IsHDEnabled()) {
        WalletLogPrintf("Upgrading wallet to HD\n");
        m_storage.SetMinVersion(FEATURE_HD);
        
        CPubKey masterPubKey = GenerateNewSeed();
        SetHDSeed(masterPubKey);
        hd_upgrade = true;
    }
    
    if (m_storage.CanSupportFeature(FEATURE_HD_SPLIT) && CHDChain::VERSION_HD_CHAIN_SPLIT) {
        WalletLogPrintf("Upgrading wallet to use HD chain split\n");
        m_storage.SetMinVersion(FEATURE_PRE_SPLIT_KEYPOOL);
        split_upgrade = FEATURE_HD_SPLIT > prev_version;
    }
    
    if (split_upgrade) {
        MarkPreSplitKeys();
    }
    
    if (hd_upgrade) {
        if (!TopUp()) {
            error = _("Unable to generate keys");
            return false;
        }
    }