iOS website jumps top the top of the page

Unfortunately, due to a lack of developer tools, mobile browsers cannot be tested in the same way as desktop browsers. Unfortunately, the emulators aren’t accurate enough.
Since scrolling is triggered by a swipe (touch), I suspect that you could, for example, slightly touch a button which then gets the focus.
This is very speculative, but worth a try.

Try ( in this case only for that page-id of https://coralstarfish-com.stackstaging.com ) in your child-theme functions.php:

function blur_all_avia_buttons() { 
if(is_page(22)){
?>
<script type="text/javascript">
window.addEventListener("DOMContentLoaded", function () { 	
(function($){
	$('.avia-button').addClass('btn-blur');
	$('.avia-button.btn-blur').on('mousedown touchstart', function(){
		$(this).blur();
	});	
})(jQuery);
});
</script>
<?php 
}
}
add_action('wp_footer', 'blur_all_avia_buttons');

Please delete the caches, especially in the mobile device itself.

or it belongs to viewport height bug on safari mobile.

try instead in quick css:

.avia-safari body {
  height: 100vh;
}

@supports (-webkit-touch-callout: none) {
  body {
    height: -webkit-fill-available;
  }
}

what was the solution? first snippet or css bug fix?