anchor links doesn't work on mobile / logo position on mobile

Hey josk-design,
Thank you for your question, for your mobile logo please try this css:

@media only screen and (max-width: 767px) {
.responsive #header_main .logo img, .responsive #header_main .logo svg {
    margin-top: 40px;
}
}

As for your anchor links #ueber_mich and #contact you have two sections for each of these IDs so the browser wants to go to the first one but it has the display none applied. You cannot have more than one element with the same id in an HTML document.
You actually have #ueber_mich as an ID three times on your page. Anyways this would cause an issue because there is not an easy way to change your menu anchor links based on the screen size, but I came up with a script that will change the section IDs if the html class avia_mobile is present on the burger menu click. This way the mobile menu items will work, try adding this code to the end of your child theme functions.php file in Appearance ▸ Editor:

function change_duplicate_hidden_ids_on_mobile() { ?>
    <script>
(function($){ 
$('.avia_mobile').on('click', '.av-burger-menu-main', function() {
  var ueberMich = $('#ueber_mich.av-small-hide');
  var ueberMichtwo = $('#ueber_mich.av_two_third');
  var contact = $('#contact.av-small-hide');
  $('#main').find( ueberMich ).prop('id', 'new_ueber_mich');
  $('#main').find( ueberMichtwo ).prop('id', 'new_ueber_mich_two');
  $('#main').find( contact ).prop('id', 'new_contact');
});
}(jQuery));
</script>
    <?php
}
add_action('wp_footer', 'change_duplicate_hidden_ids_on_mobile');

Best regard
Mike