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 AddWatchOnlyInMem(dest);
}
bool LegacyScriptPubKeyMan::AddWatchOnlyInMem(const CScript &dest)
{
    LOCK(cs_KeyStore);
    setWatchOnly.insert(dest);
    CPubKey pubKey;
    if (ExtractPubKey(dest, pubKey)) {
        mapWatchKeys[pubKey.GetID()] = pubKey;
        ImplicitlyLearnRelatedKeyScripts(pubKey);
    }
    return true;
}
bool LegacyScriptPubKeyMan::AddWatchOnlyWithDB(WalletBatch &batch, const CScript& dest)