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.
{
    WalletBatch batch(m_storage.GetDatabase());
    for (const CScript& script : script_pub_keys) {
        if (!have_solving_data || !IsMine(script)) { 
            if (!AddWatchOnlyWithDB(batch, script, timestamp)) {
                return false;
            }
        }
    }
    return true;
}
std::set<CKeyID> LegacyScriptPubKeyMan::GetKeys() const