Aggregate in C# returns nothing?

Question

I made a direct query on the console that returned me what I expected, the query in Mongo is like this.

db.AtividadeResultMongo.aggregate([{$unwind: "$LsVariaveisProcesso"},
    {$match: {
        IdAtividade : 913,
        IdEstadoInstanciaAtividade : 6,
        LsVariaveisProcesso : { $regex : /^idato/i }
    }},
    {$project: {
        LsVariaveisProcesso: 1
    }},
    {$group: { _id: "$LsVariaveisProcesso" }},
    {$count: "total"}])

when I execute return me total : 113 which is correct, has values at the base, but in the C# nothing returns and I need help to set it up in c#, someone can help me?

I tried to start like this

var agg = ObterCollection("AtividadeResultMongo")
          .Aggregate()
          .Match(new BsonDocument { 
            { "IdAtividade", "913" }, 
            { "IdEstadoInstanciaAtividade", "6" } });

var teste = await agg.ToListAsync();

but in the variable test has nothing, the connection is correct with the base is correct, I ran a Count and returned value

ObterCollection("AtividadeResultMongo")
       .AsQueryable()
       .Count()