Model function acts weird in laravel 5.1 on Live Server

I have a weird issue with Models and their eloquent relations. The thing is that I have 2 Models , User and Subject. They are linked through belongsToMany relation like so :

class User extends Model {
   public function allowed_subjects()
   {
       return $this->belongsToMany(Subject::class);
   }
} 

and

class Subject extends Model { 
 public function users()
   {
     return $this->belongsToMany(User::class);
   } 
}

the pivot table is named to convention "subject_user" and has "user_id" and "subject_id" fields. I defined a function in User class to check if the user has a certain subject like so :

public function hasSubject($subject='') {
$match = false;
if(is_string($subject)){
if(!empty($this->allowed_subjects)
                {
               return $this->allowed_subjects->contains('name',$subject)? true : false;
                }
        return false;
    }
   elseif(is_integer($subject))
   {
         if(!empty($this->allowed_subjects)
             {
                 return $this->allowed_subjects->contains('id',$subject)? true : false;
             }
         return false;
     }
  elseif(is_array($subject))
   {
       foreach($subject as $sbj)
         {
           if(is_integer($sbj))
             {
               $this->allowed_subjects->contains('id',$sbj)? $match = true : null;
             }
           elseif(is_string($sbj))
           {
               $this->allowed_subjects->contains('name',$sbj)? $match = true : null;
           }
          else{
              continue;
         }
     }
    }
return $match;
   }

The function is working fine locally , but once I hosted the app in a DO server , It acts so weird , that hasSubject always returns false even if the user has the subject . So I run its tests and they return all green . I defined a route to test this function live like so :

Route::get('/hasSubject', function(){
   $cuser = \Auth::user();
   //foreach($cuser->allowed_subjects as $sbj){
       //echo $sbj->id." ".$sbj->name."<br>";
   //}
   echo "<hr>";
   dd($cuser->hasSubject(1));
 });

and then the magic happens , if I uncomment the foreach loop , it returns true (which is correct), but when it's commented , it return false and this is the case in all my controllers , if I print allowed_subjects before calling hasSubject it works fine , otherwise no . I am really losing my mind

via Chebli Mohamed