@MrLucky this sounds familiar. If you have a chance, can you try adding this code to your site to help us narrow down the issue?
You can drop it in wp-content/mu-plugins/temp-useragent-fix.php or in your active theme’s functions.php file, and that will be enough to test:
<?php
add_filter( 'http_headers_useragent', function( $ua ) {
return 'WordPress/' . get_bloginfo( 'version' ) . '; ' . get_bloginfo( 'url' );
} );