Answers for "An invalid form control with name='beacon_serial' is not focusable"

an invalid form control with name='' is not focusable

add novalidate in your form
Example:
<form action="" novalidate>
</form>

An invalid form control with ... is not focusable.

Just because a form control is hidden doesn't mean it isn't required. And since
it is required, but hidden the browser can't focus the form control.

Every place you have .hide() change it to .hide().prop('required',false) to fix 
your problem.

An invalid form control with name='' is not focusable.

if(document.getElementById('hidden_field_choice_selector_parent_element'.value==true){
    document.getElementById('hidden_field').removeAttribute("required");        
}

An invalid form control with name='beacon_serial' is not focusable

To solve the problem, if you have a button on your page that does 
something else other than submit or reset, always remember
to do this: <button type="button">