EF Core Saving error for two objects depending on a second equal one

I have a vey long long POCO class ("FichaCliente") that I'll simplify here emphasizing the property that's an ObservableCollection:

{
  public int FichaCliente1 { get; set; }
  public int FichaClienteN { get; set; }

  public ObservableCollection<Reclamado> Reclamados { get; set; }

  public int FichaClienteN+2 { get; set; }
  ...