Expected behavior

When sending form to server and use the 'hiddenName' attribute of the datepicker, the server should get the input name in the 'formatSubmit' specific format.

Actual behavior

Now the server recives the correct format of the 'formatSubmit' but the key is: "undefined_submit" => "2020-06-09". I can mention that I have 2 datepickers, and the same result is even with one. Also tried with default examples from documentation, but I get the same result. I am using Webpack for compilation (default one from Laravel 7)

Resources (screenshots, code snippets etc.)

$('.datepicker').datepicker({
    format: 'd mmm, yyyy',
    formatSubmit: 'yyyy-mm-dd',
    hiddenName: true,
});

<div class="md-form md-outline input-with-post-icon datepicker my-2">
            <input 
                            placeholder="Choose" 
                            type="text" 
                            name="check_in"  
                            id="check_in" 
                            class="form-control">
                        <label for="check_in">Check In</label>
        <i class="fas fa-calendar input-prefix" tabindex="0"></i>
   </div>