Bootstrap Navbar disappears on mobile after using it once - html

Question

I have an issue with my Bootstrap Navbar. When I use the navbar on a mobile device, it disappears after the toggledown.
Here is my code for the navbar:
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap#4.6.0/dist/css/bootstrap.min.css" integrity="sha384-B0vP5xmATw1+K9KRQjQERJvTumQW0nPEzvF6L/Z6nronJ3oUOFUFpCjEUQouq2+l" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap#4.6.0/dist/js/bootstrap.bundle.min.js" integrity="sha384-Piv4xVNRyMGpqkS2by6br4gNJ7DXjqk09RmUpJ8jgGtD7zP9yug3goQfGII0yAns" crossorigin="anonymous"></script>
<!--Navbar-->
<nav class="navbar navbar-expand-lg navbar-light fixed-top" id="navbarSupportedContent">
<a class="navbar-brand" href="#">Ewert Loitz Personenberförderung</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="true" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav ml-auto">
<li class="nav-item active">
<a class="nav-link" href="#">Startseite <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item">
<a class="nav-link" href="#ÜberUns">Über uns</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#Fuhrpark">Fuhrpark</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Kontakt</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Karriere</a>
</li>
</ul>
</div>
</nav>

Answer 1

The outer <nav class="navbar navbar-expand-lg navbar-light fixed-top" id="navbarSupportedContent"> and the inner <div class="collapse navbar-collapse" id="navbarSupportedContent"> share the same id navbarSupportedContent. (In fact, elements with the same id are not allowed in HTML.)
All the elements with the id navbarSupportedContent are collasped accodring to the data-toggle
and data-target attributes defined in the <button> after clicking the it, including nav#navbarSupportedContent, so the whole navbar disappers.
All you need to do is to remove id="navbarSupportedContent" from the <nav> element.
Ref: https://getbootstrap.com/docs/4.6/components/navbar/#supported-content