Even with ". Asnotracking" error happens "cannot be tracked because Another instance with the same key value"

Question

public class ProcessoOsOperacaoEntity
{
    public int? Id {get; set; }

    public int? IdProcessoOs { get; set; }

    public virtual ProcessoOsEntity ProcessoOs { get; set; }

    public int? IdUsuario { get; set; }

    public virtual UsuarioEntity Usuario { get; set; }

    public int? IdPatrimonio { get; set; }

    public virtual PatrimonioEntity Patrimonio { get; set; }

    public DateTime Inicio { get; set; } = DateTime.Now;     

    public StatusOperacao? Status { get; set; }

    public decimal? Qtde { get; set; } = 0;

    public int? IdReinicio { get; set; }

    public virtual ProcessoOsOperacaoEntity Reinicio { get; set; }
}

using (var rep = new DataContext())
{
    var op = rep.Operacoes.Where(w => w.IdProcessoOs == _processoOs.Id &&
                            w.IdUsuario == _usuario.Id)
                .OrderByDescending(od => od.Id)
                .FirstOrDefault();

    if (op != null) { if (op.Status != StatusOperacao.Pausa) { op = default; } }

    var operacao = new ProcessoOsOperacaoEntity
    {
        IdProcessoOs = _processoOs?.Id,
        ProcessoOs = _processoOs,

        IdUsuario = _usuario?.Id,
        Usuario = _usuario,

        IdPatrimonio = _patrimonio?.Id,
        Patrimonio = _patrimonio,

        Inicio = DateTime.Now,
        Status = StatusOperacao.Executando,
        Qtde = 0
    };

    rep.Add(operacao);

    if (op != null)
    {
        op.IdReinicio = operacao.Id;
        op.Reinicio = operacao;

        rep.Update(op);
    }

    rep.SaveChanges();
}

I recover a record from the bank and create a new one. Inside the old one I try to put the created record in the restart property getting the error:

The instance of entity type 'ProcessoOsOperacaoEntity' cannot be tracked 
 because another instance with the same key value for {'Id'} is already being tracked. 
 When attaching existing entities, ensure that only one entity instance with 
 a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging'
 to see the conflicting key values.