Try to use this script (been used for preventing scroll with custom modals), .menu-button-class and .menu-class-name should bechanged on classnames that you have:
<script>
Webflow.push(function() {
$('.menu-button-class').click(function(e) {
e.preventDefault();
$('body').css('overflow', 'hidden');
});
$('.menu-class-name').click(function(e) {
e.preventDefault();
$('body').css('overflow', 'auto');
});
});
</script>