It seems when we have arrays and variables with upcased names, nestml generates the code without any problem, but the code won't compile for the following reasons, but first let's demonstrate the problem.
Again, we start with a simple model that should cause the problem:

neuron names_conflicts:
    state:
      Y_1 real = 42.
      x[N] real = 1.
    end
   
    parameters:
      N integer = 1  # array size
    end   
  end

Here, we have an array x and a double variable named Y_1, and the generated C++ block for the state struct is the following:

 struct State_ {
    enum StateVecVars {
      Y_1 = 0,
      X = 1,
    };
    double Y_1;
    std::vector<double> x;

    State_();
  };

Y_1 was declared twice, first as part of enum and then as double in the same State_ struct, thus the compilation of the code won't be successful, and the compiler throws the following error: ` double names_conflicts::State_::Y_1 conflicts with a previous declaration´.