Asp.Net Core WebApi returning object list

I'm trying to return a list of a "Plan" Template which has a list of "Expenses", returning only the list of plan works, but when I add to return the list of expenses of an error in javascript.

"Failed to load resource: net :: ERR_SPDY_PROTOCOL_ERROR"

"Uncaught (in promise) TypeError: Failed to fetch"

Controller

    [HttpPost]
    public IEnumerable<Plano> GetPlanos()
    {
        return db.GetPlanos()
            .AsEnumerable();
    } 

Expenses Model

[DataContract]
public class Gastos
{
    [DataMember]
    public long Id { get; set; }
    [DataMember]
    public string Descricao { get; set; }
    [DataMember]
    public TipoFrequencia Frequencia { get; set; }
    [DataMember]
    public TipoGasto Tipo { get; set; }
    [DataMember]
    public DateTime? Data { get; set; }
    [DataMember]
    public double Valor { get; set; }
    [DataMember]
    public Plano Planos { get; set; }
}

Plan Template

[DataContract]
public class Plano
{
    [DataMember]
    public long Id { get; set; }      
    [DataMember]
    public List<Gasto> Gasto { get; set; }
    [DataMember]
    public int Moradores { get; set; }

}

Call in javascript

componentDidMount() {
    fetch('Plano/GetPlanos', { method: 'POST' })
        .then(response => response.json())
        .then(data => {
            console.log(data);
            this.setState({ lista: data, loading: false });
        });   
}

Query in database

    public IQueryable<Plano> GetPlanos()
    {
        return _contexto.Planos
                    .Include(p => p.Gastos);                        
    }

Not even this console.log runs, the error happens before, if I take [DataMember] from the list of expenses it works.