Ok. I was able to reproduce the error in my enviroment. Here's the problem. You gave the name models to you factory but called it as if it was a state. $factory->defineAs (Not documented) does not define a factory with state but just give a name to your factory. Factory States and Named Factories (yours) are two different things. This is why you can't seed your database like it was a State Factory.
factory(User::class, 50)->state('models')->create();
If you want to use $factory->defineAs function, replace the above line with
factory(User::class,'models', 50)->create();
Or
(Recommended - Because it's well documented) If you still wish to be able to seed your database using ->state('models') (states), then change your UserFactory.php as follows
use App\Models\User;
use Faker\Generator as Faker;
use Illuminate\Support\Str;
$factory->define(User::class, function (Faker $faker) {
//everything works fine here
});
$factory->state(User::class, 'models', function (Faker $faker) {
//exactly the same return except for a few string values
//but 'Unable to locate [models] state for [App\Models\User]'
});
Remark: you now define your second factory with $factory->state and not $factory->defineAs.